With only five hours left, the clock races toward the climactic series finale as Jack stops at absolutely nothing to avenge the emotional setback of losing his beloved partner Renee Walker. Meanwhile, the administration attempts to keep the historic and pivotal peace agreement on track as undermining forces surface.

Will’s return to the Upper East Side continues to stir up problems for Serena, Lily and his long-standing rival, Rufus. Serena and Jenny’s relationship is strained as a result of Jenny’s deception. Blair spends time on the Columbia campus and realizes where she truly belongs…. Dan learns that Vanessa has been keeping yet another secret from him.

When Leonard and Penny aren’t speaking, Sheldon goes to extremes to keep them both happy.

Nathan and Haley struggle with the aftermath of her mother’s death, while Brooke deals with the fallout of Alexander’s tryst with Victoria. Alex discovers a secret about her leading man, Josh, that could derail Julian’s film, and Clay is confronted by an unhinged Katie.

A jewelry heist ends in murder; Delko returns to find the culprit when evidence is stolen from the lab.

Sarah and Chuck train under Laura and Craig Turner (Swoosie Kurtz and Fred Willard), a married CIA team with an impeccable record but stormy relationship; Casey trains Morgan.

Jeff and an overly enthusiastic Audrey interview a potential surrogate mother (Jaime Pressly); Russell makes fun of Adam and Jennifer’s wedding Web site.

Kat follows Patrick around when he starts acting strangely; Bianca believes Joey has an eating disorder and stages an intervention.

When Ted and Barney jeopardize Robin’s new relationship by professing their love for her, Robin realizes that she is finally over them. Meanwhile, after spending a weekend sleeping in twin beds, Marshall and Lily decide to get twin beds at home.

Valens partners with Rush to locate her abducted, drug-addicted sister, while Jeffries tries to bring justice to the case of a murdered teenaged girl that has haunted him for 17 years.

The team investigates the 1989 case of a prom queen who may have been intentionally killed in a hit-and-run; Rush tries to ignore her father’s requests to give her sister (Nicki Aycox) another chance.

Increasingly frustrated by his role campaigning for war bonds, Basilone convinces the Marines to allow him to train troops headed for combat. Transferred to Camp Pendleton, he enjoys a whirlwind romance with an initially reluctant female Marine, Lena Riggi. But the couple know they are living on borrowed time, as Basilone is soon to take part in the Marine landing on Iwo Jima.

Claudia Joy runs into an old friend while visiting a college campus with Emmalin; Roland prepares for Sara Elizabeth’s first birthday; Pamela weighs her options about divorcing Chase.

Hank’s volatility forces a confrontation with Jesse; Skyler pressures Walt to make a deal; Gus faces severe consequences.

Angie comes face to face with her ex, Patrick Logan, after years on the run. Meanwhile, Gaby and Susan plan an elaborate scheme against their husbands, Lynette sees a darker side of Eddie, and Bree meets a woman who knows Sam all too well.

Rallo gives Cleveland Jr. tips on how to woo the girl of his dreams; Cleveland challenges her boyfriend to a rap battle.

When radiation is released into the city, authorities suspend civil liberties; tired of being blonde, Lisa dyes her hair a darker color.

The Walkers seem to all being going through an adjustment period, as Cooper acts out against Sarah while Luc becomes a member of the family, Justin has trouble finding the same passion for medicine that he had while serving in Iraq, and Kevin struggles with his newfound unemployed status.

Brian and Stewie are up locked inside a safe for an entire episode.

The crew calls upon a brilliant mind from Earth to help in a crisis — a quadriplegic scientist who temporarily takes over Wray’s body.