Originally Posted by Simon
This one really made me think, and I don't think I quite have it yet. I was about to give up completely.
1. Bac4 (creates mate threat at a2) Bd2
2. Nb4 (covers the b2 square, and now Black must move his bishop off the second rank) Bxc3
3. Qg1+ (the bishop at c3 is pinned and cannot defend)
I think again 2...Kb2! is the great defender.
Not sure how Nb4 'covers' the b2 square? Perhaps you meant some other move? Anyway 1.Bac4 do not cut it...