Sarah joins forces with an unlikely and untrustworthy ally, following a trail of clues that she hopes will lead her to the origins of the clone experiment. Cosima and Delphine make a discovery that could prove to be the key to treating her illness. Alison finds herself in unsavory company at rehab.

A mystery box challenge quickly becomes a nightmare for some; while an invention test goes like a dream for others.

As Sarah and George are about to host their engagement party, Sarah confides to her Aunt Peg her darkest secret. Elizabeth needs Prudence's help in her vendetta against Sarah.

With the Tesseract now in the hands of the Cosmic Skull, the world is in catastrophic peril. Iron Man realizes teaming up with the rest of the Cabal might be their only chance for victory.

Kieren is feeling conflicted about seeing Simon secretly behind Amy's back. Simon manages to prove how much he cares for Kieren by agreeing to go to Sunday lunch at the Walker house. Amy sees them on their way to Kieren's house and is devastated by their betrayal.