It is white to move.
- ... Qxb8 loses, so why not 3. ... Kxe4? Then 4. Qxh8 is disastrous for White (4. ... Bc4+), so maybe 4. f3+, but after 4. ... Kxf5, Black should be fine. My eye's not sharp enough to find White's continuation.
- c5+! Ke6, 2. f5+ Ke5, 3. Qb8+!!! Qxb8, 4. Ke3! Black has no defense against 5. f4#