Sacrifices will be made and both universes may never be the same again after Walter and Olivia visit the "other side".

Olivia travels to the parallel universe with Walter, who faces-off with William Bel.

Peter teams up with Sheriff Mathis on a mysterious murder case; Walter faces the possibility of being sent back to St. Claire's; someone from the ``other side'' visits.

Walter deals with upsetting news and tells Olivia's niece a fairy tale.that includes musical performances by Olivia and Agent Broyles.

A shape-shifting embryo is discovered; Peter shares a family secret with Olivia.