Cozy Mysteries are distinguishable by a likable everyday hero, a tightly woven plot that engages the mind, and well cast characters formed with depth.
The character solving the crime is often an amateur sleuth who becomes involved because of personal reasons. This person uncovers the criminal through an emotional or intellectual examination of the scene, the suspects, and the clues. The main character may tell the story in the first person or in the third person. Many cozies invite the reader to solve the crime first and clues are given throughout the pages.
The victim in a cozy should not be someone who is terribly missed. Cozies are, for the most part, feel good stories. Murder is wrong, but someone had to die for the plot to get underway. The criminal in a cozy is usually motivated by human traits of greed, jealously, or revenge. You won't find many serial or thrill killers in cozies. The criminal may commit a second crime during the story, but again any violence takes place between the lines and not on the page.
Supporting characters in a cozy can be eccentric, exasperating, or entertaining. They don't have to be likable but none are so outrageously evil that they might cause the reader to stop reading. These people include the suspects (of whom the criminal is actually one), innocent bystanders, and those who may help the main character.
While Agatha Christie popularized the small English village as a setting, cozies can take place anywhere. Typically, a cozy has a small setting so that the pool of suspects is limited and relationships can be developed. Since the main character does not usually have access to forensic laboratories, the solution of the crime depends on talking to characters who all know each other.
The cozy is often a puzzle where all the pieces are available for assembly, even if the one which points at the killer needs to be flipped or examined more closely. The precipitating crime either occurs before the story starts or soon after it begins. The main character becomes involved (happily or not) and sets out to solve the injustice. As the sleuth gathers clues and gossip, there may be a threat which increases tension.
There may also be fear that a second crime might occur, and it might. The cozy is not a roller coaster ride as much as it is an examination of human frailty. Instead of unexpected plot twists, cozies are known for surprising revelations. In the end, the main character, and justice, prevail.
While graphic sex is out, romance may play a part in the cozy. If the romance starts to be as strong as the mystery, the story crosses over into another sub-genre of mystery: romantic suspense.
The final thing you will like about cozies is their delicious covers.