Peter Davison recounts what it takes to be the ultimate companion. Meeting with cast and crew past and present, Peter travels the UK and the USA in search of the answers.

While members of the 2nd Mass attempt to dig out a shot-down Beamer, Tom and a small team follow the Volm to a supply cache in search of equipment to expedite the process. Along the way, they encounter a friend, and must decide whether or not to trust her. Back at camp, Maggie and Ben grow closer as he teaches her to hone her new skills, while Pope and Sara continue to clash, resulting in a fight from which they may never recover.

Frank grapples with haunting memories from his past and his erratic behavior gets called into question, putting his team’s loyalty to the test. The Hill receives a visit from a famed physicist, whose sudden arrival sparks curiosity among the scientists – and Charlie is assigned to escort him around the compound. Callie plots an escape.

After Hendricks bans Masters from using black participants in his study, Masters contacts a journalist to promote his efforts, using the debunking of sexual stereotypes as the lure. Johnson is forced to accept DePaul's choice to end her chemotherapy treatments. Gene uncovers the truth about Betty and Helen's relationship. Libby fires Coral after discovering she lied about Robert.

Go behind the fix and see how Avi gets Manuel out of the country with Darryl's help in this companion webisode to episode 206.

Ashley asks Ray to go to bat for her friend Steve Knight, a self-help guru who beat up a waiter. Avi and Lena help Ray make contact with Volcheck to seek his aid in taking down Cochran. Mickey gets a stipend from Ray, but hopes for a bigger payday when he meets with movie exec Debra Gerson. And Bridget argues with Ray and Abby about a gift from Marvin.

Rachel and Chandler ask for six volunteers to participate in human trials of her vaccine, but the tests could be a living hell as the virus and the vaccine do battle inside their bodies. Meanwhile back in the States, Chandler’s wife and father are doing everything they can to keep their family alive.

Kevin fears he's losing touch with reality after finding himself, inexplicably, in a difficult situation involving Patti Levin, a leader of the Guilty Remnant. Meg loses control during another encounter with Matt; Jill confronts Aimee about her relationship with Kevin; Nora stands up to Laurie, and finds her privacy invaded.

President Westwood and First Lady, Gabrielle, announce the two hundred lottery finalists and prepare for the opening night reception. Vanessa uncovers a startling truth connected to the kidnapping in China. Things become dangerous as Alison and James get closer to uncovering clues about the fertility crisis. Kyle and his ex-wife Tracy appear in court to fight for custody of Elvis.

After warning Kelly to leave the city with Zack ahead of the spreading plague, Eph is arrested by the FBI. Eichhorst has one final job for Gus. Setrakian realizes that the coming eclipse is the tipping point for virus infection and the beginning of the end.

Joanna and Alex must put their past aside and focus on finding the Mandragora. Freya asks Dash to help save Ingrid. Skeptical of Freddie’s loyalty, Wendy is wary of his actions.