Ed McBain's 87th Precinct: Heatwave (1997)

"Detectives endure record-breaking heat while seeking a rapist/killer who assaulted a female officer during a stakeout."

It is a very hot summer in the city as the well known detectives of the 87th Precinct investigate serial rapes and a mysterious homicide (which do not appear to be connected). The women getting raped appear to be raped by a rapist who has raped them earlier and who was not caught. Detective Eileen Burke, who is working together with detectives Carella, Meyer and Brown, goes undercover and pretends to be one of the women who was raped earlier in order to lure out the rapist. Her boyfriend, Det. Kling, is not happy with her assignment.