Think of how pleasant it would be if you were allowed from time to time to make two consecutive moves without interruption by your opponent. You could use the first one to bring your bishop in position to attack the enemy queen, then on the next move play BxQ. Or you could use the first move to capture a protected enemy piece, and then use the second move to retreat before being recaptured. These marvelous possibilities are realized in the form of attack known as the discovered check.
We have seen that in a usual discovered attack the unmasking piece is sacrificed or otherwise creates a time-consuming threat—often a check—so that the unmasked piece can capture something on the next move. A discovered check reverses the pattern: the move by the bishop or other unmasking piece exposes the enemy king to a check from the stationary, unmasked piece. After the king avoids the check, the unmasking piece gets to make a second move—perhaps a capture or a retreat after a capture already made. This rearrangement of power between the masking and unmasking pieces makes the discovered check especially devastating, because it means that the unmasking piece in effect gets to make two consecutive moves unmolested.
This section starts with simple one-move discovered checks, then shows how the methods examined earlier in the chapter apply in this setting. In addition to discovered checks, we also will be looking at a few other patterns where the unmasked, stationary piece provides the distracting threat (even if not with a check) and the unmasking piece does the damage. In all cases you still are looking for the same kernel: a bishop masking a rook or queen. What’s new here is that you may need to draw the king into position to be attacked by your stationary piece rather than your mobile piece; and when you create a target for the mobile piece, you think a little differently because you have greater liberty: you look for ways to exploit the special opportunity to make two unfettered moves with the same attacker. The examples will make all this more concrete.
In the skeletal position to the left we have the idea in simplest form. White has the kernel of a discovered attack on the c-file. If the bishop moves, Black’s king is in check and will have to move, allowing the bishop to make a second move. The bishop’s target, of course, is Black’s queen. The bishop has two ways to attack it: Bg8 and Bd3. Either way the queen is lost. If Black moves his king, White plays BxQ; if (in reply to Bg8) Black plays Qc2, White has RxQ.