Chuck Versus the Helicopter

As Chuck Bartowski continues to come to grips with his newly adopted life as a spy, tension builds between his recently appointed partners Sarah Walker and John Casey. When a doctor who seems to have a solution to Chuck's problem is killed, Casey and Walker turn the blame at one another. Both agents persistently try to convince Chuck that the other one is responsible and now it is up to Chuck to decide which one to trust. Who will he choose?