The True Blood and Newsroom star will appear in the second episode, which features a flashback to how the doctors were rescued from the mountains after the plane crash. Porter will play Dr. Ramsey, the Boise Hospital doctor that treats the survivors after the crash.
The ninth season picks up two to three months after the Stranded Six Five (RIP Lexie!) were rescued following the plane crash. The second episode will jump back in time to show how they were rescued, while the Debbie Allen-directed third episode will jump back to the present timeline, which will find some doctors outside of Seattle Grace with new jobs.
Fans might recognize Porter as the demanding mother of Tara (Rutina Wesley) on True Blood or as Kendra James, the booker for "News Night" on Newsroom. She joins previously cast Grey's guest stars, including Tina Majorino, Gaius Charles, Camilla Luddington, Dominic Hoffman and newcomer Tessa Ferrer.
Grey's Anatomy returns Thursday, Sept. 27 at 9/8c on ABC.