8 
7 
2 
a 
b 
c 
d 
e f g 1 h Why it works
Black has just played 6...h6, attacking the bishop and expecting it to move. 7.Nd5! ignores the attack. The knight hits the queen on e7, and the bishop turns out to be poisoned: 7...hxg5 8.Nxe7 simply costs Black the queen. So Black takes on f3 with check first, but after 8.Qxf3 the queen is still attacked and the e4 pawn now looks free, with check on top. 8...Qxe4+?? seems to solve everything at once: the queen escapes the knight, grabs a pawn and forces a reply. But the queen trade is exactly what White is playing for. After 9.Qxe4+ Nxe4, the natural recapture, comes 10.Nxc7#. The knight on d5, ignored for three moves, mates on c7: Black's king never left e8, boxed in by its own bishop on f8 and pawn on d7, while Bg5 covers d8 and e7. Declining the recapture does not help either: 9...Be7 is mate in one as well, and 9...Kd8 leaves Black a queen down.
Refutation
8...Qe5 is the best try: the queen steps off the square the d5 knight attacks and keeps an eye on e4, so there is no queen trade and no Nxc7. It does not equalise: White is close to +2 here, and 6...h6 has only loosened Black's kingside. But Black stays on the board instead of being mated in two.