1. N:f4 looks like it defends everything, but it still leaves the initiative in Black's hands. And appearances can be deceiving. Black can still play 1...N:h3 2. N:h3 R:h3+ 3. gh Qg3+ and mate soon.

So White has to defend actively, with 1. R:f4 R:h3+ 2. gh Q:h3 3. Kg1 Ne6+ (Black must prevent Q:g8+, and 3...Nf3++ is no better at preventing the K's escape) 4. Kf2 and White's K escapes the mating net, with an easy win.