Ep 24. Moonstone

Nearby a lunar moon base, three astronauts find a spherical white stone which is, actually, an alien space craft containing the intellectual elite ones which flee from the imperialistic rulers of their homeland that wish to conquer the galaxy by absorbing all the knowledge. Instead of a rescue ship that they have expected, it's the warmongers' one that stop by and ask for them. They decide to commit suicide to save the base and therefore the whole world.