Professor Evil owns a time machine, and he's been ripping off all the best historical items (treasures!) from times both past and future. Your team has been charged with confiscating these items and returning them to their proper locations in time, so you now need to infiltrate the mansion and abscond with four items before Prof. Evil can secrete four of them in locations inaccessible to you. Thankfully the old soul is a bit daft and won't evaporate you should he catch you lurking through the mansion, but simply scoot you out the front door where he'll forget about you immediately.
Note that you can't just grab a treasure, however. Professor Evil can't be in the same room (of course), but you also must ensure that all the traps shown on the treasure are currently deactivated. The game board starts with eight traps on it — half active, half not — and you'll play tug-of-war with Professor Evil over keeping them in this status. Collect a treasure, and a new one will be added to the game board; collect four treasures before Prof. Evil does, and you all win Professor Evil and The Citadel of Time.