«The Big Scam: A Novel of the FBI» by Paul Lindsay

Inside a nondescript cinder-block building in Manhattan, beyond the misleading sign that reads "Global Fish" and the attractive plainclothes FBI employee at the reception desk, Special Agent Nick Vanko is running a surprisingly successful undercover operation. His bosses consider him a hard case and the members of his squad a bunch of self-destructive freaks with disciplinary problems. But despite the regular investigations by internal affairs, the squad is capable of doing real Bureau work. They've been chipping away at the Brooklyn mob, where their prime target, the don's anointed capo, Mike Parisi, is in the middle of a bitter power struggle with underboss Danny DiMiglia. DiMiglia is ruthless and unimaginative, but Parisi is smarter, and when Manny, one of his crew, finds twenty grand and a page from a hand-drawn map in his father's abandoned safe deposit box, Parisi realizes he's got the means to bring DiMiglia down. But first they have to retrieve the other half of the map, and it's in an evidence room at the FBI.
While the agents at Global Fish obstruct the FBIHQ inspector who's just arrived, a female agent is assigned to the squad. Sheila's got as many problems as the rest of them, but the most serious is her obsession with a serial murder investigation she's been unable to solve. Vanko is rattled by his attraction to her and diverts the squad to help her find the killer, just as Parisi uses the map in a whopper of a scam to keep DiMiglia in check.