With Optimus Prime having lost all memories of his life as a Prime and psychologically reverting back to his time before the war as Orion Pax, Megatron manipulates him into joining the Decepticons with the intention of using him to decipher records seized from Iacon. As the Autobots try to track Optimus Prime, Jack learns from Ratchet that the card key is connected to Vector Sigma and that they must find a way to get to Cybertron. They ultimately decide on using the Decepticon space bridge to return to Cybertron, but must locate it first. Starscream returns to theNemesisand manages to steal energon from the vault, but when a Decepticon walks his way, he hides in the closest room, where Orion is seen working. He immediately adresses him as Optimus Prime and aims his missiles at him.moreless
Ted and Barney considers the pros and cons of raising a baby together. Meanwhile, Robin hopes to dissuade Marshall and Lily from moving to Long Island.
While the Autobots continue their battle at the Earth's core, Jack learns more about Optimus' history on Cybertron.
The Autobots team up with a surprising ally to save Earth.
The Autobots discover that Dark Energon is responsible for Earth's recent natural disasters.
When the Autobots learn of the Decepticons' plans to build a Space Bridge, Optimus decides to face Megatron once and for all.
Gwen still works on getting her father out of the overflow camp, while Esther and Rex remain trapped in the San Pedro Overflow Camp. Back in L.A., Jack approaches PhiCorp in hope of finally finding answers.moreless
During a battle between Bulkhead and Breakdown, Breakdown is captured by Silas and his M.E.C.H. agents so they can dissect him to better understand Cybertronian biology. Figuring Megatron won't mount a rescue for a fellow Decepticon, Optimus Prime assembles his team to do so, much to Bulkhead's shock. Initially, he refuses to help his archenemy, but Miko convinces Bulkhead to go, so he can get a long awaited rematch against him. Bulkhead is first to find Breakdown and the two must work together to escape the savage M.E.C.H.moreless
The BAU is called to apprehend a killer who has struck Detroit for the past three years during Devil's Night, the notorious pre-Halloween celebration.