Zero at the bone

the long version

"After witnessing a mob hit, surgeon Jack Francisco is put into protective custody to keep him safe until he can testify. A hitman known only as D is blackmailed into killing Jack, but when he tracks him down, his weary conscience won't allow him to murder an innocent man. Finding in each other an unlikely ally, Jack and D are soon on the run from shadowy enemies. Forced to work together to survive, the two men forge a bond that ripens into unexpected passion"--Publisher description.