As the « Avenging Angels » change code inside New Cap City, Daniel is able to track them down, but an early snafu in trying to reach out to Zoe leave the Graystones to enter the game only under its strict rules. With only one chance, Daniel asks help from Sam who has no interest in disturbing his brother’s peace of mind.
Amanda tries to get more information from Clarice, but can’t get close enough. In order to provide her with the equipment to do so, Duram would have to give her up as his CI, a dangerous confession given the possible leak within the department.
With the world on the brink of war and chaos all around, is there anyone who can stand up to Anna? Ryan has been kept in isolation on the mothership, away from his hybrid baby so that Anna can experiment on her. Chad, seeking redemption for being used by Anna, now wants to fight with the Fifth Column. Erica goes on a journey to find a scientist who can give her the answers to what Red Sky is, and where she learns the horrifying secret of what the V’s are doing on our planet.
Afraid they will never get pregnant, Lily and Marshall decide to see a specialist. Robin begins her new job.
Lily and Marshall receive shocking news that has a profound impact on the gang. Ted begins his duties as best man for an old friend’s wedding.
Abed wakes up in stop-motion animation making him believe that the group must re-discover the true meaning of Christmas. With the help of Professor Duncan, the group explores Abed’s winter wonderland and soon discovers the truth behind Abed’s madness.
When the Fringe Team investigates a case where a victim had his heart extracted, it’s just the beginning of a series of mysterious and reanimating events tied together. Meanwhile, Peter comes to terms with the reality of his relationship with Olivia.
At Luke and Manny’s first school dance, Jay and Phil take them to the mall which turns disastrous, Claire’s is jealous when Gloria joins the school dance committee. Cameron and Mitchell learn about Lily biting other kids at the playground.
As the Warehouse team prepares to celebrate the holidays in snowy South Dakota, Pete and Myka are called upon to hunt down a malevolent Santa Claus. Meanwhile, in time for Hanukkah, Artie and his estranged father, Isadore Weisfelt reunite after 30 years.
When Ted’s new friendship with Zoey tests the theory that single men and married women can’t be friends, he invites her husband, « The Captain, » to hang out with them. Meanwhile, Marshall and Robin decide to spend alone time together, and Barney and Lily possibly have a fight.