The second book of the Diagnosis: Murder franchise.
Mr. Staniford's daughter was kidnapped, and her pinky was left on the kitchen cutting board. He got the ransom money together and delivered it as instructed by the kidnappers; and it turned out she had already died due to the conditions the kidnappers left her in, unintended by them.
Five years later, Mark and Steve are on vacation in Hawaii. One day when they are on the beach, a local restaurant owner dies in what appears to be a shark attack; however, Mark finds evidence the next day that the death was actually murder. The murderer, Wyatt, gets all the information he can about Mark and Steve, and installs listening and tracking devices on their phones and cars. Mark finds out that the murder victim was one of the four kidnappers of Mr. Staniford's daughter. Can Mark stop the murderer and get the other kidnappers alive?
"The Death Merchant" displays symptoms of the following tropes:
- Absence of Evidence: Mark is convinced that the shark bites on Danny Royal's body occured after he died due to the lack of blood in the surrounding tissue
- Accidental Murder: The kidnappers had no intention of killing Mr. Staniford's daughter.
- Antagonist Title: Mark's primary goals are to catch Wyatt (the death merchant) and to arrest Wyatt's intended targets alive.
- Better to Die than Be Killed: Wyatt prefers to commit suicide than be arrested for his murders.
- Buried Alive: Mr. Staniford's daughter was put in a storage container, which was buried with a tube to bring in more oxygen. Several bottles of water were also placed in this container to allow her to drink. The kidnappers thought she would survive there.
- Continuity Nod: Wyatt reads about Mark's major cases, including the Sweeney bombings, the air crash of Pac Atlantic Flight 224, and The Silent Partner.
- Dirty Cop: Wyatt is a former police officer, and he generally ignored suspect's rights. He resigned from the force when a pedophile he caught got acquitted; the pedophile died a few months later, from what appeared to be an accident.
- Driven to Suicide: Mrs. Staniford made two suicide attempts due to her feelings of guilt over her daughter's kidnapping and death.
- Finger in the Mail: The daughter's pinky was left on the cutting board.
- Hero Does Public Service: Even on vacation, Mark spends much of his time giving medical service. In fact, his first meeting with Danny Royal is treating him for a jellyfish sting.
- Hitman with a Heart: Wyatt is a hitman who only kills people who (at least by his standards) are evil.
- Inside Job: The kidnapping was done by four employees of Mr. Staniford's company.
- Let Off by the Detective: Although he knows that Mr. Staniford hired Wyatt, Mark decides not to try and prove it.
- Make It Look Like an Accident: Wyatt generally does this. Not with the third kidnapper, though.
- Outliving One's Offspring: Mr. Staniford found his daughter's dead body. Five years later he's hoping that her killers will be killed themselves. His wife had still been alive, too - she made two suicide attempts due to her feelings of guilt.
- Professional Killer: Wyatt kills those who have done serious crimes against rich people, and the rich people pay him for it.
- Reverse Whodunnit: The reader is introduced to Wyatt long before Mark is, and several scenes of the book are from his point of view.
- Serial Killer: Wyatt commits 3 murders during this book, and is implied to have done several others
- Shark Fin of Doom: Subverted. As part of the "shark attack" on Danny Royal, a fake fin of a tiger shark is displayed.
- Significant Anagram: Kidnapper William Gregson vanished after the kidnapping, taking on a new name. However, he created a company called Roswell Imaging.
- Threatening Shark: Subverted. Danny Royal's death appears to be this, but is later discovered to be murder.
- The Villain Must Be Punished: Wyatt is clearly motivated by this - starting with not caring how he got evidence while still a police officer, continuing with his apparent murder of the pedophile who got acquitted even though he was guilty, and up to his last words before he died, making sure Mark won't let the fourth kidnapper escape justice.
- Witness Protection: At the end of the book, Dr. Plume - a plastic surgeon who helped wanted criminals get new identities - gets placed in this program in return for helping catch these criminals.
