8/1Kn1p3/1p5N/4p1q1/4k1N1/3R2p1/Qn2B3/7R w - - 0 1
The key move is the second one. Alena gave the key line above when black plays 1. ...Qf4- 2.Kb6 is the only solution after that point.
Looks like 1. Rh4 threatening 2. Nf2 dbl ch and mate does the trick.
- Rh4 Qxh4
and White is going to make with 3. Qb4 or 3. Qxe5
It is an amazing move- the second one- it opens the white king to 7 different checks on black's second move, and all 7 are answered with mate. Unfortunately for me, I never really focused on 1.Rh4, and never really gave myself a good chance to find the solution.
Another 15 minutes
At first I have found mate in 4. Then I guessed how to mate in 3.
I'm very surprised but it took me 30 minutes. At first I got stuck on Qb1.
After that I corrected my solution and got mate in 3.