Mr. Monk and the Dirty Cop - 9780451226983

Captain Stottlemeyer relies on obsessive-compulsive genius Monk to solve his most baffling cases. Of course, most of the credit and attention goes to Monk - but Stottlemeyer is okay with that. At least, that's what he says.
Stottlemeyer is feeling a little frustrated. When the captain is faced with budget cuts, Monk's fees are one of the expenses he trims. He claims it's nothing personal, but Monk and his assistant, Natalie, suspect otherwise. Monk even offers to help out at no charge, but Stottlemeyer will have none of it.
Monk has no hard feelings and is too compulsive to stop investigating. He resorts to calling in tips under assumed names. (After all, who would ever guess who Adrian Smith, Adrian Jones, and Adrian Brown are?) The captain is infuriated ... and so is Natalie, who would like to see Monk, and herself, get paid for the consulting services.
But when Stottlemeyer is arrested for the killing of another cop - with overwhelming evidence against him - he turns to the only detective who can possibly prove his innocence: Adrian Monk. That is, if Monk can overcome some potentially crippling obstacles along the way.