The solution is rather complex: 1.Ne4+ this threatens Be1 mate so the Knight cannot be taken 1...Kh4 2.Ng3 (threatening Nf5 mate) and the three main lines are:-

1. 2...fxg3 3.Bb6 and now we have reached a position where if 3...Qa1+ 4.Bg1 and if any pawn which can move defended by the Queen does move then the Bishop sacrifices itself for that pawn and if the Queen takes back it is stalemate because the g1 square is then covered by the Queen so white is stalemated. If the queen sacrifices itself for the Bishop on g1:- 4...Qxg1 5.Kxg1 then the king can simply mop up the pawns who have to move because the Black king and other pawns have no moves. But then Black is stalemated. So its drawn.

2. 2...Kxg3 3 Be1 mate 

3. 2...Qf8  the solution to this is 3.Be1 threatening Nf5 mate so 3...fxg3 is forced when 4.Bf2!! either gets a stalemate if 4...Qxf2 or gets into the same theme as the mainline if Black doesn't take or finally if 4...gxf2 comes 5.g3+ Kxg3 stalemate. If Black plays Qf3 at some stage White just ignores it and keeps his bishop on the a7-g1 diagonal, and then if Qxg2 then Kxg2 again traps the Black King.