The doctors treat dozens of people when the roof of a romantic restaurant collapses on Valentine’s Day; Meredith struggles with her new duties as the chief’s wife.

Derek begins his role as interim chief. Teddy refuses to place Cristina on her service. Arizona tests Alex out in pediatrics. Mark refuses to speak to Lexie.

Derek confronts Richard for the sake of his friend and the hospital. Izzie returns, hoping to reconcile with Alex. Tensions run high between Teddy, Cristina and Owen.

Desperate to help his pregnant daughter, Mark follows Addison to Oceanside. Derek’s suspicions are raised when the Chief recruits Meredith to assist with a high profile operation.

Thanksgiving, Christmas and New Year’s pass. Miranda is visited by her father. Mark and Lexie cope with the arrival of a woman from his past. Thatcher questions the Chief’s behavior.

Izzie returns to Seattle Grace with an important figure from her past. Stress takes a toll on Richard. Owen recruits a fellow Iraq war vet as the a cardiothoracic surgeon.

All eyes are on Arizona to help a patient with an enormous donation to spare. Cristina tries to test Owen’s boundaries, and Alex is losing it over Izzie.

A recap of last night’s Grey’s Anatomy, the aptly-titled “Invasion.” It was a brutal one for fans of our favorite characters.

Derek must help the most unlikeliest of all; the hospital lab-tech, Isaac, when it turns out that he has an inoperable tumor surrounding his spine. McDreamy also questions Richard’s authority.

An episode guide to last night’s Grey’s Anatomy, “Tainted Obligation.” It was a good one!