The Infinity Train theme is a recurring sequence of four notes (high D, B, high G, F sharp) that plays at the start of almost every episode of Infinity Train, minus the premiere episodes "The Grid Car," "The Black Market Car," "The Musical Car," and "The Twin Tapes." However, it serves as the main leitmotif for "Running Away," the theme for Book 1 and thus the opening of "The Grid Car," and can be heard over the main title card in "The Musical Car" and "The Twin Tapes."

The song, and variations of it, serve as a recurring riff throughout the series' soundtrack, generally appearing in sequences where the Infinity Train appears to passengers.

History

In-universe, it is the tone used by Amelia and One-One to control or summon the Steward and Porters.

Trivia

• The song is a direct reference to a musical sting from "The Mysterious Stranger" segment of The Adventures of Mark Twain (which itself was a direct inspiration for Infinity Train) in a sequence where Satan destroys a miniature civilization he had just brought to life.