Synopsis: In orbit of the library world of Biblios, the Vromyx and Garynths are engaged in a battle to determine the fate of the planet. Each species is jealously guarding the secrets of legendary super-weapons from the other. Neither side will believe the library's caretakers that there are no such secrets to be found inside. The Doctor must thus think quickly of a way to bring peaceful resolution to the dispute. He finds an empty warehouse on the library's grounds, and rigs it with explosives. Then he calls up to the commanders of both sides and tells them that's where the records are housed. As the fleets move closer, the Doctor destroys the warehouse. With nothing left to fight over, the two fleets end their battle and go home.
Synopsis: A human survey team arrives on an alien planet. So does the TARDIS. Both crews discover a beautiful world, with friendly humanoid inhabitants. As the Earth team watches the locals, though, they see what they believe to be an act of human sacrifice. One person willingly places himself in giant spider's web, apparently awaiting the day when he'll be the spider's meal.
Horrified, the Earth team begin killing all the spiders to make the planet safe. The Doctor probes a little deeper though, and discovers a humanoid apparently hatching from an egg. The Doctor rushes back to the Earth team, only to find out that the spiders have now all been killed. Sadly, in so doing, the humans have permanently destroyed a beautifully symbiotic ecosystem. The humanoid inhabitants of this world didn't "sacrifice" themselves to the spiders. They gave food to the spiders, who, in turn, provided cocoons for the humanoids, from which the humanoids would metamorphose into humanoid butterflied.
The Doctor leaves, saddened that he could not work out what was going on in time to save this fragile relationship.