A veteran salesman is forced to make way for a young drummer and has some improbable adventures along the way in this comedy-drama. Eddie (Robert Forster) has worked for over 30 years as a travelling jewelry salesman, but after he's stricken with a heart attack, he discovers he's no longer eligible for insurance. Given the fact that he routinely travels with a stash of goods worth up to a million dollars, this development means that he's going to have to give up working on the road. Bobby (Donnie Wahlberg) is the young salesman who is first in line to take over Eddie's route. Though Eddie doesn't think much of reckless Bobby, he takes him on the road to show him the ropes. As they spend some time together, Eddie takes a liking to Bobby, who wants to show Eddie his gratitude for teaching him how to sell in the big leagues. Bobby takes him to a combination roadhouse and brothel for an evening's entertainment, but things get sticky when jewel thieves track the two men to the club. Diamond Men also features Bess Armstrong and Jasmine Guy as a pair of working girls Eddie and Bobby meet in the course of their adventures.