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.
Synopsis: In the future, the Millennium Wars are raging. The Doctor materializes right in the middle of one battle in a corner of that war. The TARDIS accidentally throws off a combatant's ship, forcing it to crash. The pilot, a soldier, figures out that the TARDIS drew him off course, and now he wants to enlist the Doctor in the war. The soldier attempts to compel the Doctor to use the TARDIS to down an enemy vessel. The Doctor--or more precisely, the malfunctioning TARDIS--does this. When the soldier rushes out of the TARDIS to go finish off his enemy, he locks the TARDIS, fixes the problem, and dematerializes--just as a second enemy ship arrives to attack the soldier.