Imaginaerum tells the story of an elderly composer, Tom, who suffers from severe dementia. As he has had the disease for years and has regressed into childhood, he remembers practically nothing from his adult life. His music, friends, all his past including the memory of his daughter are a blur in his fragile mind. All he has left is the imagination of a ten year old boy. As he drifts away into coma, it seems impossible to get back what he has lost. Or is it?

After a quick courtship, two lovers hastily decide to tie the knot. As their first year of marriage unfolds, temptation and incompatibility put their relationship in jeopardy.

Harry Williams, member of the rhythm & blues band, Bloodstone, is about to go onstage for a concert when he is hit on the head. The rest that follows is his dream. The four band members become conductors on a train filled with characters and (impersonated) actors from the 1930s, such as W.C. Fields, Dracula, and Scarlett O'Hara. Various songs are featured. The singing conductors are obliged to solve a mystery; Marlon Brando is murdering Nelson Eddy, Jeanette McDonald and others by suffocating them in his armpits. A wacky funeral, a fight with a gorilla, and the threat of being turned into a wax museum figure are all part of Harry's dream.