Phil invites his old high school girlfriend over; Jay accidentally kills Manny's pet turtle and tries to cover his tracks; Mitchell stands up to his boss.
Stan loses his confidence after a car salesman gets the best of him; Roger and Steve try to get to first base with the popular girls at a makeshift drive-in.
Steve creates a robot that matches him in appearance and demeanor, but chaos ensues when the mechanical being attempts to obtain Laura by any means necessary.
Steve tries out for the basketball team only to end up as the equipment manager; Laura gets snubbed by fellow cheerleaders and seeks advice from Steve.
Sheldon contends against President Hagemeyer's boss over science requirements; Mary discovers that Georgie is working at Meemaw's illegal gambling room.
Sheldon contemplates on how to stop thinking as he struggles to focus; George Sr. visits Brenda Spark's house to take over the handman responsibilities.
Sheldon arrives at his dorm and is delighted to find that he has been assigned a room all to himself; an unwanted partner goes into business with Meemaw.
The gang learns that Rachel is pregnant; Joey tries to impress a Broadway director who's dating Chandler's mom; Chandler's shoes make it hard for him to dance.
Joey finds a sweater from a one-night stand that Rachel had a month ago and deduces that it belongs to the father; Joey proposes to both Phoebe and Rachel.
Ross and Rachel argue over who initiated their latest tryst, so they go to Ross's video to prove who came on to who; Monica and Chandler talk about honeymoon.
Joey sets Rachel up on a date with one of his co-stars, which doesn't sit well with Ross; Ross discovers that a coworker of Chandler's has been calling him Toby
Once realizing that his future of ever getting close to Penny will never be, Leonard decides to engage in a one night stand with a fellow female scientist.
After being invited to a physics conference to present his findings with Leonard, Sheldon refuses to attend the event as he does not want to share the honor.
After purchasing a coveted time machine prop from a classic 1960 film, the guys are excited about its arrival, but the object causes problems for Penny.
When Sheldon's twin sister Missy visits, Leonard, Wolowitz and Koothrappali become infatuated with her, and Leonard comes up with plan to eliminate the others.
Penny tries to plan a surprise birthday party for a reluctant Leonard, but she gets sidetracked when Sheldon tries to live his fantasy in an electronics store.
Claire gets Phil to agree to sell the old family station wagon; Mitchell decides to build a princess castle for Lily; Manny invites a girl over to study.
Gloria decides to cook more traditional Colombian meals; Claire finds out that Alex likes a boy; Mitchell and Cameron fight over Mitchell's aversion to PDA.
Claire becomes a neighborhood vigilante to stop a speeding car; Phil tries to land important listing; Jay teaches Manny to ride a bike; mysterious neighbor.