The natural move for Black is 1. …Ng4—natural because it creates a mate threat on h2 (when your queen attacks a square next to the enemy king, adding another attacker against that square is always something to consider). How will White respond? His options are limited; he has to add protection to h2, and his only way of doing so is 2. Qf4. This seems to successfully parry the threat against h2, so now what? Well, notice that the White king is sealed onto h1; this should provoke thoughts of a smothered mate. White’s queen guards the mating square (f2), but it also guards the mating square h2. So again it’s overworked, inviting you to play one threat followed by the other: first comes 2. …Qxh2+; 3. QxQ; then the smothered mate 3. …Nxf2.