Three astronauts return from a flight into outer space, only to find that one of them has disappeared entirely. When they returned they were all there, but then one gradually disappeared. First he couldn’t see himself in the mirror, then his parents didn’t recognize him on the phone, then he simply vanished. Then when he was gone, one of this cohorts didn’t recognize him.
Now the second member of the crew seems to be disappearing as well, and the third member doesn’t believe him, thinks that he is undergoing some form of trauma. The first crew member’s thoughts that perhaps they shouldn’t have come back at all, that maybe someone - or something - let them slip through its grasp is coming true, and now they are vanishing from reality. Slowly each of the members is erased from existence, and even the experimental plane is simply gone.
Look for a small appearance by Sue Randall as the nurse. She also appeared in From Agnes with Love in Season 5.