Ryan, the Cohens, the Coopers and their friends build new lives, resolve lingering issues, face major decisions and undergo shocking personal transformations. No matter what happens or where they go, the members of this unique extended family all know that they will always have one another to turn to.
In the aftermath of a major earthquake that cuts off power and communication between the Cohens and their loved ones, Seth must take over Ryan's role as the protector when Ryan is injured and the boys are stranded on a deserted road. Elsewhere, Summer and Taylor worry about their missing boyfriends while searching for Summer's escaped pet rabbit - and the quake leads to an unexpected reunion for Taylor.
Taylor eagerly prepares for her first real birthday celebration, but she frets over the fact that Ryan has still not told her he loves her. Even more concerning is the fact that she has secretly applied to and been accepted at Berkeley, the same school Ryan is going to attend. Summer helps Taylor come up with a plan to help Ryan express his feelings. Meanwhile, Kaitlin misbehaves outrageously in reaction to Julie dating Frank.
Newly engaged Seth and Summer both panic about the prospect of being married, but neither will break it off, despite the advice of their friends. Instead, they begin a complicated game of one-upmanship that almost leads them to Las Vegas for a wedding. Meanwhile, when Ryan's estranged biological father, Frank who has been in prison for years, tries to reconcile with Ryan, Sandy remains dubious.
As the new year approaches, Ryan plans a special surprise road trip for Taylor and himself, but when Summer confronts Seth about not making any plans, Ryan's romantic getaway for two is spoiled. Later, Summer's future rests in the hands of a shady character that the gang meets on the way to Las Vegas. Meanwhile, Julie's accounting practices come under some unwanted scrutiny.