Deadline: 2 A.M. — Robert L. Fish

To save a fellow cop, a detective is asked to free a hardened thug 

For most of his life, Pop Holland has carried a .38 revolver. This afternoon, when he retired from the San Francisco police department, he said goodbye to the gun forever. But when he steps into his car on the way to his retirement party, he feels the familiar shape of a .38 pressed to his neck. The gun cuts into his skin, and blood runs down his back. Another man gets into the car, handcuffs Holland's hands and feet, and takes him into the night.
 
A half hour later, homicide lieutenant James Reardon sips cognac, waiting for Pop to arrive at the party. The phone rings, and the kidnappers whisper the news: They have Pop, and he will be dead by morning if Reardon disobeys their instructions. They are willing trade Holland for one of their own, a criminal who deserves to spend the rest of his life behind bars. To save one life, Reardon must contemplate putting countless others at risk.

Deadline: 2 A.M. is the 4th book in the Lieutenant Reardon Mysteries, but you may enjoy reading the series in any order.