Asshole Victim: the victims in Fiddlers become less sympathetic when you discover just what rotten people they were, and what they did to Charlie to make him so deranged. Michelle, the main victim in Romance, is a whiny, spoiled diva who gets her boyfriend / agent to stab her for attention and is later stabbed for real.
Bad Ass: Steve Carella, Hal Willis, Cotton Hawes. Lt. Byrnes, Meyer, and Kling have their moments too.
Badass in Distress: Carella is kidnapped, chained to a radiator and injected with heroin in Doll.
Berserk Button: Emma is Brother Anthony's in Ice. And vice versa, as the novel's killer ultimately finds out when he murders Anthony...
As a father of a teenage daughter, Meyer absolutely hates paedophiles and has to be cautioned by Carella in Lullaby when dealing with the father of the murdered baby, who was having an affair with the other murder victim - the 15 year old sitter.
And in Lady, Lady, I Did It!, when Carella, Brown and Kling go to arrest the killer, Kling loses all control and beats him half to death, because one of his victims was Kling's girlfriend Claire Townsend.
Best Served Cold: The main plot in Ten Plus One and Fiddlers. In the former, the killer is targeting people who were in a play with his wife at university, and who participated in an orgy-turned-gang rape during the aftershow which left her infertile. In the latter, the killer is targeting people who screwed him over in some way, from his own mother - who abandoned him and his brother - to a teacher who refused to give him an A and made fun of him.
Brick Joke: Meyer's long, wonderfully orchestrated story about cat thief in The Mugger.
Broken Bird: Eileen Burke, so very much. She becomes a cop after her father and uncle, both policemen, are murdered, and dreams of avenging her uncle's death. She is raped and slashed in one book and suffers PTSD as a result, and it gets worse after the events of Tricks, when she shoots a man who was killing and mutilating prostitutes, after he tried to kill her.
No Kill Like Overkill: Pepe Miranda's death in See Them Die. First, he is shot repeatedly by the army of cops. Then Andy Parker empties his gun into him. And then, Parker grabs another gun and shoots Miranda in the head. Twice.
Non Sequitur: Meyer often blurts his (unrelated to the topic at hand) thoughts out loud, confusing the others.
Not-So-Harmless Villain: some of the most mild and harmless-seeming people turn out to be killers, such as Timothy Moore, the victim's medical student boyfriend in Ice.
Meaningful Name: Usually averted, but played straight with Don King from King's Ransom.
Scary Black Man: Arthur Brown, and he's more than happy to play on white people's prejudices (see Jigsaw for an excellent example). Unfortunately, some white suspects have a tendency to talk to the white cop who's interviewing them (usually Kling) and ignore Brown completely.
Unintentionally Notorious Crime: In Lady, Lady, I Did It, a shooter opens fire in a store and guns down four people. One of them happens to be Detective Bert Kling's fiancee, thereby guaranteeing that the crime has the attention of every cop in the city.
Where The Hell Is Springfield? / No Communities Were Harmed: The series takes place in "Isola", a borough or district of an unnamed city in an unnamed East Coast state. As mentioned above, it's clearly meant to be a stand-in for NYC (which nonetheless exists as a separate location in the series' universe).