Chess Opening Theory/1. e4/1...e5/2. Nc3/2...Nf6/3. Bc4/3...Nxe4/4. Qh5

Vienna Game, Falkbeer Defence
Black is threatened with Qf7#. They have seven legal moves that prevent this - surely one of them must allow them to avoid ruin?


 * 4...Qe7 and 4...Qf6 allow Nxe4 winning a piece, as without the queen to defend d5 the fork trick has had its prongs bent.
 * 4...g6 allows Qxe5+ picking up the knight or the rook.
 * 4...Ke7 allows Qxe5# picking up the game.
 * 4...d5 gives the pawn back for nothing as after 5. Bxd5 the threat is renewed.
 * 4...Ng5 is met by 5. d4 forcing the knight to e6. Even if knight and king both survive the subsequent complications, White can regain the pawn and enjoy a whopping lead in development.

So by a process of elimination, it has to be


 * /4...Nd6/

Which has the enormous attraction of attacking the undefended c4 bishop.

Theory table
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1. e4 e5 2. Nc3 Nf6 3. Bc4 Nxe4 4. Qh5