Bethesda have released four screens and some details on the upcoming fifth downloadable episode fpr Fallout 3 - Mothership Zeta. It will release on PC and Xbox 360 on August 3, with PS3 owners needing to wait slightly longer (no date yet).
Here is a short description of the story:
"A strange Alien signal is being broadcast throughout the Capital Wasteland, originating from a crashed UFO. Is it a distress call, or something far more sinister? That question is answered when you find yourself beamed aboard an enormous Alien spacecraft, with only one alternative - to fight your way to the bridge of the ship and secure your escape."
Here are some bullet points on what to expect:
"- Find and exploit new and destructive alien technology, like the Alien Atomizer and Drone Cannon.
- Explore the vast Mothership and learn the secrets of the Aliens' master plan.
- Thwart the Aliens' attempt to stop your escape, and take over the Alien ship before it wreaks havoc on the unsuspecting Earth below.
- Fight against the Alien Invaders, their robot drones, and turn their own horrible experiments against them.
- Ally yourself with an unexpected array of characters, both from the Capital Wasteland and from Earth's past."