Sam and Naomi are against each other to lead the practice with unexpected results. Addison treats a girl trying to hide her past while Cooper has a dilemma of his own affecting his professional career.
The BAU investigates a series of murders that appear to be connected to a killer who jumps trains and chooses his victims based on their proximity to the railway.
Giant guinea pigs are attacking cities all over the world. The boys have the key that will save everyone from the onslaught but they're stranded in the Andes Mountains.
The CSI team investigates the shooting death of an archaeologist whose secret life may have caught up to him.
Matt grapples with his mother, his emotions and Coach Taylor as McCoy garners more attention. Tami tangles with Tyra about Julie and Tyra's interest in Cash. Tyra experiences Cash's darker side. Erin disappoints Jason.
A baby with AIDS has Benson and Stabler asking for assistance from Warner as they investigate the case. They are pointed in the direction of a homeopathic doctor who has an questionable ethical past and who had prescribed the baby ineffective vitamins.
With Lucas back within MI5 he reveals that the Russians interrogated him about Operation Sugar Horse, the most secret ongoing spy operation MI5 ever had. If the Russians know about it, then MI5 has a very high level mole. Harry seeks out his mentor, The Spycatcher, to help him find the mole. Ben is undercover with an Al-Qaeda cell; they are planning to bomb London and what looks like a dry run unexpectedly turns live.
After recuperating from her health scare, Adrianna returns and tries to make amends with Naomi, but her ex-BFF refuses to forgive her for the betrayal. Adrianna makes a surprising connection with Navid, who helps her through her situation. Meanwhile, Annie and Ethan finally take their rapidly growing romance to a new level during the school's homecoming dance, causing Naomi to feel jealous.
San Francisco lawyer Eli Stone begins to see things, which leads him to discover a brain aneurysm. But his visions lead him to accept cases with little monetary gain but a lot of moral goodness.
Gibbs and his team are searching for a cyber serial killer who takes videos of his victims. The team quickly finds out that the video's of the dead victims are false.
Vic closes in on Shane, Mara and their sick young son; Claudette dismantles the Strike Team; Pezuela offers Acevada "assistance" for his mayoral campaign; Rita Denton (Frances Fisher) comes on to Dutch; and Billings' ex-wife and daughter are fearful when a registered sex offender moves into their neighborhood.
An ailing man suffers from blackouts and sleepwalks, leading the team to wonder if his sleepwalking is a symptom, or how the man is becoming exposed to something else. When the man's daughter grows ill as well, the team must provide a diagnosis before both die. Meanwhile, Cuddy adopts a newborn but when the birth mother displays a rash, she has to make a decision between putting the mother or daughter at risk.
When a girl is found covered in blood and holding the murder weapon that killed her best friend, she becomes an obvious suspect, though she can't remember anything. But Jane, believing she's innocent, engineers a risky maneuver in which she must relive the terrifying events in order to spark her memory.
The team must shift their attention from a case they are working on and hand it over to Martin, after a child is reported to have been kidnapped at a mall.
Alien pods are discovered in an abandoned garage; a retirement-home resident has a deadly gift; a patient wishes to be reattached to his formerly conjoined twin; a power-company employee confronts a scientist who is stealing power to create the ultimate weapon.
Casey is in panic mode after the diary that details her unsettling romantic dreams about Truman goes missing. Believing that Derek and Edwin took it, Lizzie and Marti attempt to get the diary back by making their stepbrothers' lives miserable.
The Suttons say goodbye to Johnny, and Charles pops the question.
Mike teams up with the boys from Bartos Bait & Fish to catch leeches that will later be sold for fish bait. Then it's off to the Green Tripe factory in Hollister, CA where Mike helps make BARF (Biologically Appropriate Raw Food) for dogs.
Desperate to regain her memory, Sam opts to join a clinical trial and starts taking pills for her memory. Sam's memories start coming back, but she doesn't like what she learns about her former self. Elsewhere, someone confuses Dena and Andrea as being a gay couple, which frustrates Andrea and sends her on the hunt to find someone hotter than Dena.
Brent thinks the self-serve option at Corner Gas will make his life easier, until he discovers his customers are enjoying it a little too much. On the other hand, Lacey’s Ruby buffet has her customers working overtime. Wanda’s quest to reclaim her title as Rumour Queen proves disastrous for Karen and Emma, while Hank’s old laptop becomes a hot potato when he tries to sell it to either Oscar or Davis.