A Peterborough Petes junior player who won the Max Kaminsky Trophy as the league's best defenceman in 1970, Plumb was drafted 9th overall by the Boston Bruins in the 1970 NHL Amateur Draft. After two seasons with the Bruins' Central Hockey League farm club Oklahoma City Blazers, he jumped to the upstart World Hockey Association Philadelphia Blazers in 1972. In the WHA Plumb became a star, winning the Dennis A. Murphy Trophy as the WHA's best defenceman in 1977, and being selected a First or Second Team All-Star for much of the league's history.