“The Full Circle” is episode fifteen of season one of Space: 1999.
Paul is trying to contact Eagle 6, which isn’t responding. Eagle 6 has landed on what looks to be a habitable world, but the ship looks empty. Dr Russell asks Commander Koenig what happened. The recon party is late and it’s hours since they last checked in. Koenig asks Paul to bring the Eagle back by remote control, then heads to the landing pad with Victor and the doctor. The Eagle seems empty, but Dr Russell finds a dead Stone Age man.
The commander is arranging a rescue mission of two Eagles. Dr Russell is taking a medical team; Dr Mathias is going to autopsy the man they found. Koenig will take Eagle 1 and a ground party; Alan will take Eagle 2 and do an aerial search. Victor wants Sandra to go with Alan to take photos. Victor himself will remain in command.
Victor and Paul are talking about the planet, Retha; they’ll be past it in three days and if they’re going to settle, need to do so before then. Victor is going to check with Dr Mathias about the autopsy.
Eagle 1 lands and the commander and Dr Russell head out on a moon buggy, finding a marker left by the reconnaissance party. Eagle 2 has spotted patches of mist, possibly smoke. The doctor and Koenig have found some huge clawed prints and, by some water, Dr Russell spots something in the bush. Koenig shoots at it. The rest of the party has arrived at the first marker. They contact Eagle 2 and tell Alan they are entering an area of mist and will try to catch up with the commander by nightfall.
Victor wants Paul to contact the commander about the autopsy. He doesn’t respond, nor does the second group. Alan responds; he hasn’t heard from either in some time. Alan is going to land by Eagle 1 for the night. Sandra thinks she saw something move; Alan doesn’t, but agrees there’s something odd. They land and more Stone Age people watch the Eagle from the bushes.
Sandra wakes to find Alan not there. She contacts him; he’s gone looking for the others and is by the moon buggy. She warns him to be careful and, after the call, he falls into a pit trap and is knocked out. Sandra tries to contact him again and fails. Victor and David are leaving in Eagle 3, which Paul tells Sandra when she tells him she’s lost contact with Alan.
Alan comes around but can’t get out of the pit. Several of the Stone Age people arrive and one jumps into the pit and attacks Alan, knocking him out again. Before Alan can be killed, his commlock goes and the Stone Age man answers it by accident, and disconnects it by accident as well. He’s helped out of the pit. Victor tells Sandra they are coming in as Alan comes around again, this time able to leave the pit.
They’ve lost contact with all the ground parties after they headed into the mist. And the Stone Age people on the planet look strangely familiar.