Beckett continues her quest to find the stolen toxin as Castle is left with less than a day to live after his exposure.
Ted and Peggy work really well together, while Pete goes looking into who Bob is and Sally goes looking at a boarding school.
A former flame of Sheriff Lamb's shows up asking for help. Savino deals with the snitch inside his casino.
Max feels obligated, as Caroline's best friend, to throw her a surprise birthday party, but when she learns all Caroline wants is to see her father, Max takes her to Jail to see him.moreless
After making a shocking discovery in the desert, Sydney agrees to submit to an experimental procedure conducted by an eccentric doctor, designed to retrieve her lost memories. But while Jack and Vaughn look on, Sydney's mind proves surprisingly resistant to letting her remember her missing time -- and the process of recovering it could end up killing her. Meanwhile, Lauren makes a great sacrifice in order to make her alibi believable to Lindsey after breaking Sydney out of NSC custody, and Sloane finds himself boxed in by an unlikely enemy -- one who wants to see Sydney Bristow eliminated permanently.moreless
Daniels sends Archer and T'Pol to 2004 Detroit to follow three Xindi-Reptilians who are creating a biological weapon.