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e f g 1 h Why it works
Taking on e4 was fine — the engine approves 6...Qxe4 — because the b4-bishop pins the c3-knight against the king; the queen sits attacked but untouchable. 7.Ndb5! threatens Nxc7+, and 7...Ba5?? answers the threat while keeping the pin: the bishop now guards c7 AND still ties c3 to e1. Perfect — except 8.Nxc7+!! happens anyway. It is not a fork, it is a deflection: after 8...Bxc7 the bishop has left the a5–e1 diagonal, the c3-knight is unpinned, and 9.Nxe4 simply takes the queen that was 'safe' for three moves.
Refutation
7...Bxc3+! resolves the crisis by trading the piece that made ...Qxe4 legal: after 8.bxc3 the queen retreats via e7/d5 next move and Black is close to fine (engine −0.6). The pin was an asset with an expiry date — cash it in before Nxc7+ ideas force the bishop to choose between its two jobs.