Explanation

In this level, you can achieve a smothered mate in three moves. Typically you can force the king into the corner with a double check, and then force your opponent to block the last escape square as you saw in level two.

Examples

White can force the king into the corner with the double check Nh6+, giving check with the knight, and discovering a check by the queen.
Black cannot capture the knight, because that would not defend against the queen check, and is forced to move the king into the corner with Kh8.
Now White can force Black to block the last escape square with Qg8+!
Black has to capture with the rook, because the knight on h6 is protecting the queen.
After Rxg8, the rook is deflected away from protecting f7, and blocks the king's last escape square.
White can then checkmate with Nf7#.

The power of the double check means that this even works if the queen is attacked, as in the following example:

White's queen on c4 is attacked by the rook on d4, but that doesn't matter.
After the double check Nh6+, Black can't capture the queen nor the knight, and is forced into the corner with Kh8.
White can then force smothered mate with Qg8+ Rxg8 Nf7#.

Related combinations

Smothered mate in three moves often makes use of the double check into checkmate, block escape square and deflection into checkmate combinations.