Shepard will use his magic maguffin on the computer of sorcery with the help of the thief, the wizard and the knight to vanquish the Reapers to the outer realms of an alternate universe (or something). Seriously though, ME's overarching plot so far has been completely generic, the actual conclusion to the whole thing probably won't be very different from that nonsense, except with a lot more running around for arse holes.