Are you writing a locked-room mystery novel? Good for you! If you need some ideas on how to write a locked-room mystery, we’ve shared 6 comprehensive tips for you below. Enjoy!
1. Have an impossible crime
A person is found dead inside a locked room. There is only one window that is firmly locked. The door was also locked from the inside. Who killed the person and why?
That is the basis of a locked-room mystery story. It always involves a crime that is seemingly impossible to commit. Normally, it will involve three types of crimes: murder, kidnapping, or theft of an important object or artefact.
It is called locked-room mystery because it always happens in a location that is impossible to get in or out without witnesses. When it is a kidnapping or theft, the room might also be guarded by a security detail who never left their spot or fell asleep, and yet the theft or kidnapping still happened.
In these type of stories, the story goes beyond the simple whodunit plot, and how the crime was committed becomes more important than who did it and why they did it (although these are important too for a good locked-room mystery story).
2. Create an investigative protagonist
As with all mystery novels, the protagonist must be the person who is going to investigate the crime (murder, kidnapping, or theft), especially if you’re writing a novel. The protagonist must lead the investigation, either privately as a PI (private investigator), or as a police chief or sheriff (depending on the location).
The protagonist must know how the investigative procedure normally goes and be able to apply said knowledge to the situation at hand. While someone close to the victim (like a family member or a friend) might be extensively involved and be a major supporting character, the protagonist should still be someone who will be able to investigate the crime. If the protagonist is the victim’s sister, or another family member, or a friend, then you need a solid reason why they are the one to investigate.
An exception can be done in the short story or novella format – wherein the protagonist (i.e. the person investigating the crime) is not someone who is a trained detective. Due to the short format, despite the impossible crime, the protagonist should still be knowledgeable enough about the possible suspects involved and about the situation at hand (i.e. the locked room the crime was perpetrated in) and be able to solve the crime due to a clue that will reveal a lot more than it seems at a first glance.
3. Know the locked-room variations
When it comes to locked-room mysteries, location is key. While nominally called locked-room mystery, the crime that is the catalyst for the story does not necessarily have to happen in a locked room.
The location can be a house, an island, a boat, a plane, an apartment, a hallway, a high balcony or terrace – any place that was inaccessible at the time of the crime would do.
For example, a group of friends go to an isolated island that is accessible only by a ferry at a certain time of the day, let’s say noon. The group of friends arrived at the island the previous day via the ferry at noon, and the next day, when the ferry arrived at noon again, all of the friends are dead – but as far as the official records show, there was no one else on the island besides them.
Another example can be a card game room. Let’s say that five people are playing a game of poker. The electricity goes out, and by the time the people sort it out and get light inside the room, or the electricity comes back, one of them is dead and the other four are suspects.
4. Have a list of suspects
Like any good mystery, you need to have a list of suspects as the possible perpetrators of the crime. The longer the story, the more suspects you want to have. The story will always begin with the crime having been already committed. However, the bulk of the story lies in the protagonist investigating each suspect and either eliminating them from the list or keeping them on it.
Each suspect should have the following three things: motive, means, and opportunity. Some suspects will have two out of the three, for example, means and opportunity, but would lack motive (and other combinations). More than one suspect should have motive on top of the means and opportunity. For example, if you have a list of six possible suspects, then at least four of them should have all three to make the investigation more difficult for the protagonist.
As the protagonist goes through all of them, they should start to eliminate them one by one. This is done by identifying which suspects have, for example, the means and the motive, but lacked the opportunity, or which suspects had the opportunity and the means, but lacked the motivation.
For example, perhaps the victim was an old man who has recently changed his will to leave everything not to his extended family, but to the nurse who was taking care of him in his ailing days. His death seems like an apparent suicide or even a heart attack, and he was alone in his locked bedroom when he was found dead.
But, the old man had three sons, two daughters, and they are all married with children. This means that there is a hugely scorned family to consider as possible suspects. Out of all of them, the easiest family members to eliminate would be those who wouldn’t need the money the old man would’ve left them.
The next family members to eliminate as suspects would be those who were on good terms with the old man and who wouldn’t want to kill him out of revenge. The next suspect, of course, would always be the nurse who took care of him – what if she knew he left her everything in his will and decided to kill him to get the inheritance?
5. Detail how the crime was committed
Before you start writing the story, you need to determine and know how the crime was committed in detail. The fun of reading a locked-room mystery, as previously stated, is not only in who committed the crime and why, but also in the how it was done.
Usually, the perpetrator will go out of their way to ensure that they are not even a suspect in the beginning of the story. This means that the victim (if the story revolves around a murder) is not going to be murdered via a method that is loud (for example, a gunshot to the chest or head), or hung – and if they are, they will do what they can to make it appear like a suicide.
In fact, suicide or a natural death (from a heart attack or another medical condition) is what the crime will normally look like in the beginning of the story. If the story revolves around a kidnapping, it would seem like the kidnapped person was not, in fact, kidnapped, but had left on their own accord.
However, you need to know the exact details of the crime and how it was done. For example, if all the doors and windows are locked, how did the killer escape from the room? What kind of trick did they pull? Did they go out via the ventilation vent in the ceiling? Is there a trapdoor or a hidden door inside the room that no one knows about and the detective has to discover?
Knowing all the details of the crime will enable you to create clues for the protagonist, but also for the readers, and when the resolution finally comes, the readers will be satisfied.
If this part is not done well, the readers will be left disappointed. Remember, your audience is a fan of both mysteries in general and of locked-room stories in particular – and as such, they will be able to see through a lackluster story. If the details of how the crime was committed do not add up, the readers will know and they will feel cheated.
6. Plant red herrings
Knowing all the details about how the crime was committed will also help you to create red herrings. A red herring is a storytelling device that is used to divert the readers’ attention and have them look for the perpetrator of the crime in the wrong direction.
On a story level, red herrings are meant to create false leads, false clues, and false suspects. The protagonist will spend some significant amount of time getting the red herrings out of the way in order to solve the crime.
However, when the red herrings are too obvious and not done well, the readers will see right through them, and these should be avoided. For example, let’s go back to that poker room of five people where one of them ended up dead after a few minutes’ blackout.
One of the suspects might be a person who has a murky background and a history of committing a lot of crimes. They are the most obvious suspect. The protagonist should easily be able to eliminate them from the suspect pool based on the fact that this person doesn’t really have a motive. Besides being a criminal in the past, there is nothing to incriminate that person.
But, if the protagonist spends too much time suspecting that person, even if it is out of personal prejudice, the reader will know that the suspect is a red herring and will be annoyed that so much time is being spent in such a wrong direction.
Good red herrings (or suspects that did not really commit the crime), will have at least a motive for committing the crime, or the means, not just the opportunity. Opportunity comes last in that specific hierarchy – meaning, a suspect without a motive or means will not commit the crime, even if they did have the opportunity to do so.