“The Last Enemy” is episode twenty-four of season one of Space: 1999 and the season finale.
Alpha is approaching two planets; they’ll be in range to survey soon. On that planet, a woman, Dione, is contacted by another who says the council has decided unanimously to strike first before the travelling moon gets any closer. Dione says that’s excellent; they’ve waited a long time. On Alpha, Victor reports that planet is inhabited. The commander orders contact procedures. Dione wants her ship, the Satazius, prepared; she’s told the crew is waiting. When she gets there, Dione is told they’ve received a signal from the travelling moon. She orders it be ignored and to launch.
Victor reports the two planets are on opposite sides of the sun to each other; they never see the other. Sandra reports a ship has been launched and David says it’s a battleship. Koenig orders the defence screens up and Eagles to launch pads. Dione is told that Alpha’s defences are up.
Koenig wants the Eagles airborne as soon as possible. When in range, every Eagle to fire simultaneously. Victor says to Koenig that shooting first and asking questions after isn’t his style. The commander says they’ve been asking questions; they haven’t been answered. Given the size, it must be aggressive. Victor tells him if they aren’t yet, they soon will be.
The Eagles are ready for lift off and Dione gives orders to neutralise them. They can’t lift-off, even on automatic. Computer can’t analyse the Satazius either, due to interference. Dione then orders Alpha’s defences be deactivated. Satazius slows to land and Dione is told there’s no sign of enemy activity. She orders the missile launcher deployed and fired. The missiles go right over Alpha, striking the second planet. Dione is told there’s been no response from Delta yet. She wants the firing positions pinpointed when there is.
Victor and Koenig realise that the two worlds can’t fire on each other. The Moon has provided them with a gun platform. Missiles are launched from Delta and the commander orders non-essential personnel to deep shelters and Eagles to bunkers. The Satazius fires back at the incoming missiles, but one looks to strike them.
Alan is now able to take off and he’s ordered to take a look at the Satazius, then pull back when a small craft deploys from it, which lands on one of Alpha’s launchpads. Koenig says they need to let them in to find out what’s going on. Heading to the airlock, they find Dione who hands over her weapon.
Dione demands sanctuary. The commander is not happy and wants her tossed off the base. Dione tells him that the Bethans could destroy Alpha easily. Koenig wants no part in their war. But, because Alphas has been used by the Bethans, the Deltans will come in response. If Koenig wants to live, he needs Dione’s help.
The Bethans and the Deltans have always been at war. Whilst the Moon passes through the system, it is a suitable firing point for a time and both sides know that. And are firing at it. Which isn’t good for Alpha, stuck in the middle. Koenig tries to negotiate with both worlds.