Chess Opening Theory/1. e4/1...e5/2. Nc3/2...Nf6/3. Bc4/3...Nxe4/4. Qh5/4...Nd6/5. Bb3/5...Nc6/6. Nb5

Vienna Game, Falkbeer Defence
With his last move, 6. Nb5, White has launched a very dangerous attack against Black's Nd6, the key piece of the defence, which is immobilized (6...Nxb5?? 7. Qxf7#). White now menaces the obvious 7. Nxd6+, leading to a forced mate (7...cxd6?? 8. Qxf7#; 7...Ke7 8.Nf5+ Kf6 9. Qxf7+ Kg5 10. Nh3+ Kg4 11. f3#).

The only solution for Black is to defend f7 with another piece, and the only one available is the Queen. However, after 6...Qe7? or 6...Qf6?, White may play 7. Nxc7+ followed by 8. Nxa8, gaining the exchange.

This material loss is unavoidable, but, before it happens, Black has the opportunity to improve his position with some intermediate moves, advancing the pawns to block White Queen's attack lines. On the other hand, White can repropose the mate threat, moving his Queen to different offensive positions. Therefore, the game continues:


 * 6...g6 7. Qf3 f5 8. Qd5

At this point, Black can no more defer the protection of f7 with his Queen, and therefore he is forced to allow the Knight fork on c7:


 * 8...Qe7 (or 8...Qf6) 9. Nxc7+ Kd8 10. Nxa8

In order to sacrifice only the exchange, and not the whole Rook, Black then plays


 * 10...b6,

preparing Bb7.

The final result of this sharp sequence is the Frankenstein-Dracula Variation.

Theory table
.

1. e4 e5 2. Nc3 Nf6 3. Bc4 Nxe4 4. Qh5 Nd6 5. Bb3 Nc6 6. Nb5