This mission allows you to steal 1 plan from storage on a planet or to steal 1 level from a building on the planet. In either case a success will give you 1 building plan should one be available. If there are no plans in storage and your spy attempts to steal a plan from there you will get a notice regarding no plans available.
If you spy attempts to steal a building level as long as there is a building with a level greater than 1 you will get a plan from that building and the building on the target planet will lose one level. The plan returned by this however can not be greater than the level of your spy, and the level of the building. So if a level 1 spy succeeds in such a theft you will get a level 1 plan even if the level that the building lost was level 30. A level 0 spy for this purpose will act as a level 1 spy.
Playing Tips: This assignment is very commonly used especially against the AI's. It allows the theft of multiple potentialy high level upgrade plans. The most prized of the plans being upgrades for glyph buildings. This tactic is refered to as Stripping. A planet is considered stripped if there is no building left on a planet greater than level 1.