Agatha Christie had a very distinctive style of storytelling. By viewing all of her stories, a notable set of characters emerges that Christie tends to use over and over again. These are not identified by name, but instead tend to be of the same type. By mixing and matching from among the stable, a new cast of characters is assembled for each story. As an example, the Housekeeper is a prominent figure that appears often in Christie murder mysteries. This "type" is usually an older woman who plays a prominent role in a early household, often developing a close relationship with some of the children. This makes her a very versatile character who often sees events from a different perspective, but is a figure who isn't related to the principals.
The other novel innovation is that they character types can play different roles, depending on the needs of the story. They can be heroic, supportive, corrupt, evil, each in turn as the story demands. To return to our example, The Housekeeper can be a totally supportive caretaker of the abandoned child, when the mother's career takes her away from the family. Or, she could be an abusive tyrant who oppressed the lonely child while the mother was away. Or she could be the real mother of the infant, who couldn't afford to raise it and so gave it to the wealthy family to adopt. Three totally different characters when written, but sharing the same basic Type in the drama.
The same "Type" of character can take on different forms, while remaining essentially the same. For example a character can be:
reversed and play against type, so that the doctor in one story might be portrayed as being incompetent, instead of highly skilled. Or as neurotic instead of reassuring and stable.
Doctors are usually highly moral and sympathetic, but can be reversed to be untrustworthy and out for their own personal glory at the expense of their patients.
Of course, any of these versions of character types can be the hero or the murderer.
Another Christie element is having two characters who are mirrors of each other. The most obvious is the Rake and the Rival, but you will find that same parallel in other characters as well. Often one of them is the murderer, or the victim. For example, two brothers - one goes off to war and is the hero while the other is the village shepherd. One character is the garage mechanic, while the other tragically hangs himself after being wrongly accused of a murder.
1. The Doctor. This man is a promising/ successful doctor but with a hint that something happened in his past that cast a shadow on his present situation. Typically intelligent, sympathetic, good in a crisis, with a developed sense of professional ethics. Can also appear as The Nurse.
One of the useful things about doctors is that in a murder set in Christie's rural countryside, the population is usually composed of country bumpkins and uneducated, superstitious folk. A doctor is one of the characters that can be relied upon to be intelligent and well educated, not given to cults and rituals, and other nonsense.
Doctors are repositories of village information about births, illnesses, deaths, parentage and various comings and going within their records. Doctors are sometimes called upon to give cause of death. They can be sources of tension and secrets, first because they don't wish to get their diagnosis wrong, which they invariably do when older patients are murdered and they put it down to heart failure. Second, their records often hold the truth about things like out of wedlock births, or lost pregnancies, or terminal illnesses which might give someone a motive for murder.
One subset of the doctor character is the Harley Street Specialist. When a character is mentioned in reference to being seen on Harley St. it is universally bad. You see such doctors when looking for impossible cures for obscure diseases and maladies, and particularly when one is looking for a secret illness that is likely terminal.
2. The Energetic Young Woman. She has history that the story will explore, but enjoys current success, possibly financially or professionally. She is often the initial instigator of the inciting action of the plot. One of her main charms is that she is just so full of life, so full of action and motion. She may be "less attractive", but she "has an intelligent face, and one can tell she's capable and energetic." Her past may be catching up with her, however, in one way or another. She can be an accomplished artist, or musician, or dancer, but she can also be a florist or another job that Christie views as suitable for an unmarried woman.
3. The Batty Eccentric. This is a character who is distinctly
odd and unusual. Their behaviors may be flighty and erratic or they may
perceive the world in a non-standard way. One might describe them as
batty, or absent-minded. Sometimes they are involved with the occult
(seances, astral spirits, ghosts). Other versions are beset with
alcoholism, or PTSD, or true mental illness. Many around them view them
with amusement, or tolerance, or even irritation and sometimes they are
dismissed and inconsequential by the murderer.
3.5 The Cloud-headed Girl. This is often a female figure who is
portrayed as slightly odd or eccentric and is universally acknowledged
to have her head in the clouds. She will often be described that way by
other characters, being "queer" or "odd", or "living in her own
world." This peculiarity is sometimes the result of an incident in her
childhood, or her odd parents, or her having been raised in isolation,
but she sees the world in a different way and those around her view her
as a kind of oddity. She may legitimately suffer from mental illness,
or may be the only person who truly sees reality for what it is.
The Cloud-headed girl is a subset of the Eccentric, though the former is usually
younger and presented as more serene and innocent, while the older
version has more direct schemes and is more assertive.
4. The Temptrix. This woman is motivated by using her feminine wiles to take what she wants or to steal another woman's husband, their achievements, their fame, their family, their property. Could be rival sisters, or schoolmates. She is a master manipulator and is typically utterly devoid of any scruples. While amoral, she isn't always the main evil of the story, and is sometimes presented with sympathy in that she's just doing what she must to get by.
5. The Young Specialist. A botanist, a photographer, a young engineer. Typically a young man who is technically gifted but socially awkward. Always an expert in his chosen field. May love hopelessly from afar. Used as a resource to supply any obscure poisons, technical gadgets, top secret plans that the plot may require.
6. The Housekeeper. Often devoted to the Lady of the house, or to the neglected children. Fiercely loyal to someone, but from her position and perspective in the household can often see details that others miss. Presented as a "salt of the earth" character, very practical and level-headed. Can sometimes appear as The Cook, or the Butler, or The Gardener (see below). Sometimes Russian or a Gypsy, or French; and if so her spoken English is not fluent.
6.5. The Maid. With similar characteristics to the housekeeper, often realized as a subset. Ever present in the house, she lurks behind curtains, appears at odd hours to turn down bedclothes, or freshen up the fire. Can go anywhere without comment but sometimes gets scolded. Typically an audience favorite. A similar character to the Footman, the Assistant Gardener, the Stable Boy, depending on the needs of the story.
7. The Industrialist. Usually a wealthy older man who is the head of a business, or a engineering company developing fighter airplanes, or working on some breakthrough chemical formula, or involved in shipping and importing goods from Japan.
8. The Legal Mind. Frequently, Christie writes her stories to involve court proceedings, or to do with the execution of Wills, or the researching of family trees and marriages. Whenever this happens, she brings in this character to be a reference to the researchers. Always very intelligent, very methodical and logical, often hindered by how much information they can divulge.
9. The Efficient Professional. This is usually a woman who is good in business, and is excellent in managing business affairs. Highly intelligent. Very smartly dressed but perhaps less warm or empathetic to those around her. Excellent in conducting research, managing large databases. A classic example is Miss Lemon. Devoted to and respected by her employer but who easily rebuffs the foolish attention of single men. Where the Energetic Young Woman is full of creative flair and social grace, the Efficient Professional is full of practicality and attention to detail yet often content to work behind the scenes in the shadow of some larger personality. While the EYW is effusive and often good with people, the EP is more introverted and reclusive.
10. The Rake. A young man who indulges one or more vices. Often is very successful at it, but it may catch up with him eventually. He may be a womanizer, or a gambler, or an addict but always with extreme flair and charisma. Usually he is brilliant in other ways, or is unreasonably charming, which hides or excuses his flaws to others. This may be a ne'er-do-well pilot, or a race car driver, or a wealthy man about town.
11. The Rival. A young man who is in competition with the main male character. Often not quite as successful, never did quite as well in school or on the sports field. This sometimes makes him bitter about life. He may have a failing that he doesn't manage well, such as drugs, gambling, alcoholism, that holds him back.
12. The Daughter. a young girl of between 7 and 12 years old. May age into another character after the Time Gap. Usually the object of affection by another character (a mother or father, Nanny or Housekeeper). May be unusually precocious and/or may die tragically and be felt as a memory or a photograph.
13. The Vicar. In every village, you'll find the resident clergyman who spends his days visiting his parishioners and learning their gossip. He is an invaluable source of information, history, and ancient artifacts. For example, he knows about all the births, marriages, deaths and those sorts of records that are kept in the church. This is also the place where ancient objects would tend to end up, stuffed up the bell tower, or down in the basement.
14. The Politician. A "stuffed shirt" more concerned about himself than anyone else. His public image and the scandal of the situation often takes precedence over personal feelings and empathy for his fellow humans.
15. The Dubious Man from India - The Overseas Connection. In the cosmopolitan world of Great Britain, our characters often have occasion to travel abroad. Christie loves to include characters who have connections to "exotic" or far flung outposts of the British Empire. And while what happens in Vegas stays in Vegas, this is not so for former travelers who come across people they met while in India, or Kenya, or Hong Kong, or Argentina, or Singapore or on the steamship home. Our protagonist might be running from an unfortunate past, but these dubious travelers are there to bring it all back up again. Sometimes a blackmailer, or simply a source of information. This character could be a retired Colonel in the army, or a Archaeologist from Egypt, or a back ally underworld figure from the streets of Bangkok, or a movie producer from Hollywood.
16. The Loving/Lonely Wife. In many stories, a prominent husband can often be stubborn and prideful. In these cases, a genuinely concerned wife can take her own initiative to try to make a situation better, often by consulting our resident detective. Often not possessed of all the facts, nevertheless she feels compelled to act, seemingly motivated entirely by concern for her husband and family.She is often presented as being very caring, but her attention is not always appreciated.
18. The Cantankerous Old Woman/ Cruel Old Man. This is the older character who is past the social niceties and practices being as unpleasant as possible to everyone around them, except possibly their favorites. This may be because she is very old, or possibly with a lingering terminal illness but she is past caring what other people think. For Christie, this is usually a female character, because her female characters tend to be more vividly drawn. When the character is male, it is usually because they have far too much money and are used to always getting what they want, never having to answer to anybody. This could be the owner of a factory who bosses everybody around or an arrogant lord of the manor who owns all the property in the village. Frequently the victim of murder.
19. The Social Outcast. This is the communist or socialist or temperance zealot that has very strong beliefs and attends "meetings" and distributes pamphlets but are really just misunderstood by society and no one takes them or their ideas seriously. Often brooding and keeps to themselves because they can't get anyone to really listen. Bonus points if they suddenly change their philosophy when they come into money or find a lovely girlfriend.
20. The Shopkeeper. A favorite is the local postmaster, who also runs a general store in the small town. They know the comings and goings of everyone because they all shop there and we read their mail. As such, they are tremendous sources of information, but typically are hard for the detective to interview because they are used to keeping secrets. They also often are involved in a shady business of their own, because of their position of privilege.
21. The Mirror. A classic Christie element is having two characters who are mirrors of
each other. These are characters who are roughly the same age, same gender and possibly social position, but choices made earlier in life have set them on wildly differing paths. In this way, they have a number of characteristics that are parallels and opposites. The most obvious is the Rake and the Rival, but you will
find that same parallel in other characters as well. It may be that the parallels are not immediately obvious because the characters are so different, until one goes looking for them.
Often, one of them
is the murderer, or the victim. For example, two brothers - one goes
off to war and is the hero while the other is the village shepherd. One
character is the garage mechanic, while the other tragically hangs
himself after being wrongly accused of a murder.
Tropes
A. The Time Gap. This is not a character but is a prominent and recurring element. Its very rare to have an Agatha Christie story that does not span over at least two generations. The entire story may be relating extended flashbacks, or we might see the protagonists as children and then as grown adults. Typically, there is an obvious jump in time between the "child" and the "adult". Sometime this time gap is wider and involved historical figures.
B. The Ominous Event. This is some event that happened in the past, some instigating action who's ramifications have cast a pall over all those involved, often an extended family or the entire population of a village where it took place. Because of this event, fortunes have been lost, careers have been scuttled, marriages have been broken, the road signs have been defaced. Because of this cloud of doom, the villagers never speak of it and it must be kept a deadly secret. Everyone knows, but nobody says anything. Except that they talk about it constantly, behind closed doors, in the nook of the snug, when they think that outsiders can't hear them. And emotions run deep just below the surface.
C. The Obscure Relationship. There is one person
whose history appears to be completely transparent, but when our hero
takes the time to investigate, discovers an obscure connection to someone
else related to the case. This could be a long-lost mother from before the war, or an aunt
who went to live in Canada, or the young man who fell in love with the house maid when the family was living in Cairo, but then he was recalled to military service, and the family had to evacuate because of the war, and when she turned up pregnant every body suspected but no one said anything, but what they didn't know was that the maid was the concealed grand daughter of King Farouk in hiding to escape the coup.
D. The Convoluted Will. A great uncle whose will at his death left a great fortune to one of the other cast,
unbeknownst to them, but only if he died before Tuesday and she
remained unmarried until her 28th birthday. There could be an Old will and a New will. Extra points if one or both is currently missing, possibly destroyed, and also possibly forged. Witnesses to the signing are often crucial to the proving of the will, but alas, they have moved to Australia.
The Adventure of Johnny Waverly: 14. The Politician.
The Hollow: The victim, Dr. John Cristow, is clearly the Rake, plagued by his wife, his mistress, and his former mistress, and he can't keep his hands off any of them. And yet he is also noble, researching cures for intractable diseases and admired by all.
Henrietta is the Energetic Young Woman, a successful artist and an independent woman who loves John Cristow but refuses to marry him for his own good.
Gerda Cristow, John's wife, is the Cloud-Headed Girl, a successful wife and the mother of two children, but continually beset with lack of self confidence, comic scenes of learning how to drive a car, and an obsequious devotion to her husband, whom she seems to constantly annoy. Often, the cloud-headed girl is portrayed as amusing, but here she is tragic.
Lady Lucy Angketell is the Batty Eccentric, constantly talking too much and saying the most inappropriate and inane things at the worst times.
Sir Henry Angketell plays the role of the Scientist/Specialist, only his fascination is for guns. As is typical, this character supplies the murder weapon.
Veronica Cray is the obvious Temptrix, a movie starlet with a history with John Cristow some 12 years ago (the Time Gap) who's not above trying to seduce him away from his wife and family. She knew John when she worked in Hollywood, California (The Overseas Connection).
Gudgeon, the classic Butler, with deep loyalty to the family
We even get a short cameo of Doris, The Maid, who reports to the police that she saw Gudgeon carrying the revolver, gets soundly Scolded for her impertinence.
Edward is the Rival with John, in this case for Henrietta's affections, whom she dismisses as "inadequate." Later, he finds success with Midge Hardcastle, the classic Second who is living in the shadow of the more forceful Henrietta. Edward knew Henrietta and Midge when they were young (The Time Gap) but could only see her as "Little Midge," the scrawny girl. Now he recognizes her for the mature young woman she has become.
Finally, Poirot is aided by the generous Inspector Grange, who values Poirot's input and brings him into the entire investigation.
Twenty Rules For Writing Detective Stories ca. 1928.
1. The Doctor.
2. The Energetic Young Woman.
3. The Batty Eccentric.
3.5 The Cloud-headed Girl.
4. The Temptrix.
5. The Young Specialist.
6. The Housekeeper.
6.5. The Maid.
7. The Industrialist.
8. The Legal Mind.
9. The Efficient Professional.
10. The Rake.
11. The Rival.
12. The Daughter.
13. The Vicar.
14. The Politician.
15. The Dubious Man from India - The Overseas Connection.
16. The Loving/Lonely Wife.
18. The Cantankerous Old Woman/ Cruel Old Man.
19. The Social Outcast.
20. The Shopkeeper
21. The Mirror
Tropes
A. The Time Gap.
B. The Ominous Event.
C. The Obscure Relationship.
D. The Convoluted Will.