From ABC's official press release:

Addison teams with Derek to save the life of his pregnant patient, as Naomi and Bailey treat Sam after a sudden asthma attack, on ABC's Private Practice.

Guest starring Grant Show (Melrose Place, Swingtown) as Archer Montgomery.

As Archer recoups from surgery, Derek has Addison work with his pregnant neuro patient; after Sam suffers a sudden asthma attack, Bailey and Naomi work together to find the root cause of Sam's sudden attack; and at Oceanside Wellness, Cooper, Violet and Pete work together to treat a mother suffering from postpartum depression, on Private Practice, Thursday, February 12 (10:02-11:00pm, ET) on the ABC Television Network.

Private Practice stars Kate Walsh as Dr. Addison Forbes Montgomery, Tim Daly as Dr. Pete Wilder, Audra McDonald as Dr. Naomi Bennett, Paul Adelstein as Dr. Cooper Freedman, KaDee Strickland as Dr. Charlotte King, Chris Lowell as William Dell Parker, with Taye Diggs as Dr. Sam Bennett and Amy Brenneman as Dr. Violet Turner.

Special guest stars Justin Chambers as Dr. Alex Karev, Chandra Wilson as Dr. Miranda Bailey, James Pickens, Jr. as Dr. Richard Webber, Eric Dane as Dr. Mark Sloan, and Patrick Dempsey as Dr. Derek Shepherd.


Source: ABC
(Image courtesy of ABC)