Sometimes, mistakes get made when it's time to reincarnate people. For one particular sucker, whose name has unfortunately been lost to time, a mistake led to them being reborn in the body of a slug-like creature. Now, they must learn to navigate life in the seas of ye olde days - long before humans were even a thought. About 550 million years before humans were even thought of.

I'm sure they would have much preferred Plan A.