After moving in with Lyndsey, Alan continues to have a rendezvous with Melissa at Charlie's house.
Barney uses his best womanizing tactics to try to convince Ted to design the new GNB building; Robin drunk dials Don.
Mordecai and Rigby find a plate that they think would look good with cake, but when they don't have enough money for any, they use Skips' upcoming birthday as an excuse to throw a party and to eat the chocolate cake at the snack bar.
Section D is forced to welcome an FSB officer onto the Grid to help track down Aibek, a rogue nationalist from the ex-Soviet state of Azakstan. Aibek is in the UK to find the last known sample of the nerve agent 'Paroxocybin'. The chase is on, but will the team find a way to stop the nerve agent falling into the wrong hands without ruining Anglo-Russian relations? Meanwhile, Lucas's personal life takes a passionate turn.
An escalating gang war spills into the stands of a high-school football game, killing several people; an unlikely partnership arises.
Mike dives into an amazing Michigan collection but Frank seems to have lost his picking mojo. The guys visit an incredible Wisconsin property that features a reconstituted vintage town. And, the only thing better than Ted’s quirky small town gas station is his one-of-a-kind home where everything is for sale. Frank senses engine trouble with the van while Mike ignores the signs and ends up on his hands and knees.
When a coded document attracts Castle's attention, Beckett must steer the case back to the violent felons who populated their victim's world; when Beckett's ex-partner arrives, Castle must watch the relationship become romantic.
Nancy decides that her family has seen enough gunslinging for a lifetime, so to lighten things up she takes them to a Montana fair. Andy and Silas enter a butter-eating contest while Doug looks after the baby and makes friends with the carneys. Elsewhere, Nancy escorts Shane on a rollercoaster where they stir up some trouble in line.
Simon and Tara pay her sister a visit at university and his friends decide to tag along. Will wants to take a look at the university. Jay decides to offer sex advice to Simon.
A monster called the Fright Hound starts attacking Crystal Cove and people believe Scooby-Doo is behind it. Could Scooby be the one attacking the city or is someone setting him up?
The CSI's must catch a madman causing havoc all over Miami and the team has to mourn one of their own.
As Mason goes in for his 6-month check-up, Kourtney realizes she wants another baby so her kids will be close in age like she and Kim were, but when she obsesses about getting pregnant, Scott thinks she's taking all the fun out of the process of trying. Meanwhile, Bruce has a hard time accepting that 12-year-old Kylie has male friends, and there's tension when she breaks the rule about inviting a boy up to her room.
Matthew Crawley and his mother Isobel arrive at Downton, and have difficulty settling in. Carson is mortified when confronted by his past. Violet attempts to promote a match between Matthew and Mary. Isobel is elected to serve on the hospital board.
Grampa gives each family member a portion of his savings; Lisa worries that Nelson's instant success with a new business venture might lure him away from continuing his education.
Lynette is angry when Renee starts spending a lot of time with Tom; Bree finds herself falling for Keith (Brian Austin Green); Susan feels guilty about her side job.
Stan offers a reward to the person who can stop Hayley and her old boyfriend from eloping.