The mage involved is researching a set of books that create a rip in the time-space reality when brought together. He wants them to see if he can create his own pocket dimension. The player is asked to help find the books, which are scattered around in various dungeons and bookstores (just pick any that already exist).
After retrieving the books, the mage does his experiment; the books and he disappear into an interdimensional rift. Daedra, random objects and animals begin filling up the house as reality starts to collapse.