Soft Target by Stephen Leather (Mass Market Paperbound)

The second book in the bestselling Dan 'Spider' Shepherd series. There's only one thing more dangerous than a corrupt cop . . . and that's a corrupt cop with a gun. When a group of armed police in an elite unit turn maverick and start to rip off drug dealers at gunpoint, undercover cop Dan 'Spider' Shepherd is given his most dangerous mission so far. Shepherd is ordered to infiltrate the tight-knit team, to gain their confidence and to ultimately betray them. Facing men with guns is nothing new for the former SAS trooper, but it's the first time he's had to investigate his own. And the job couldn't have come at a worse time for him. As Shepherd finds himself in the firing line, he has to decide exactly where his loyalties lie.