Fringe: Season 3, Episode 10

3 - 10: The Firefly

A series of events leads Walter to befriending musical icon Roscoe Joyce (Christopher Lloyd), keyboardist of Walter's favorite band, Violet Sedan Chair. Walter learns through the Observer September that bringing Peter from the parallel universe ultimately, though a long chain of events, led to the end of the band due to death of Joyce's son. The Fringe team is unaware that September has engineered events in the present to test Walter's resolve to let go of Peter when the time is right.