Having successfully settled the survivors from a Underfell and Underswap Underground, Glenda Adams Soleil and Sans reunite to find their missing robot dog Jake, discover the source of the ichor and put a stop to it before more universes are compromised, and return to reality J-27 to rescue Asriel. Meanwhile, Asriel resumes his exploration of the Deep with his golem friend, Golemite.

Book 4 of the Otherwhere Legacy, preceded by 'Undertale Everdeep I: Deeper'.