Ah, treachery! - Ross Thomas

Having been 'allowed' to resign his commission after punching out his senior officer in El Salvador, Edd Partain launches himself into civilian life with crushing indifference. His new job hardly pays the rent and won't even stretch to a renewed membership of VOMIT (Victims of Military Intelligence Treachery). It's a job he can't afford to lose, but lose it he does when his employer is paid a visit by the slimy Colonel Millwed, who tactfully informs the store-owner that he is employing a psycho. Sadly for Edd, she's ignorant of Millwed's hidden agenda: the small matter of the theft of $1.2 million of CIA funds. Intended for the Salvadorean army, the cash went walkabout in 1989 and now Edd's one liability the thieves can do without.
Razor sharp and dead (pan) funny, AH, TREACHERY! once again proves that no one writes thrillers like Ross Thomas.