The story of a sometimes disobedient small green locomotive who worked for the Merioneth and Llantisilly Rail Traction Company Limited, although he dreamed of singing with the Grumbley and District Choral Society. In time he became first bass of the choir and transported the members from place to place.

His driver was Edwin Jones, known as Jones the Steam, who enjoyed fishing and daydreaming. Ivor's other friends included stationmaster Dai Station, portly choirmaster Evans the Song, fellow chorister Idris the Dragon, and fairground owner Morgan the Roundabout. Mr Morgan gave Ivor some pipes from his steam calliope to allow him to sing in the choir.