DONT (Disturbing Opponents' No Trump) is a conventional defense used after an opposing 1NT opening. It sacrifices the natural penalty double in order to show all possible one- and two-suited hands.
After an opposing 1NT:
|X||Any one suit (5+ cards), relays to 2|
|2||Clubs and a higher suit (At least 4-4 in the two suits)|
|2||Diamonds and a higher suit|
|2||Hearts and a higher suit (spades)|
|2||5+ spades, weaker than a double followed by a 2 rebid|
After hearing a double, partner is expected to bid 2, which is completely artificial. (He may, however, bypass the 2 relay and bid a very strong 6-card suit of his own.) The 2 bid allows doubler to then show his suit: he passes with clubs and bids his suit otherwise. A jump bid by either player is strong and invitational, but not forcing. A raise of doubler's suit is also invitational but not forcing.
After hearing a 2 or 2 overcall, partner usually passes with support for the bid suit; otherwise, he can bid the next-highest suit to try correcting the contract. For example:
The 2 bid denies support for clubs and asks for overcaller's other suit. With diamonds, overcaller passes; with a major, overcaller bids it.
A 2NT response by partner at any time is strong and forcing for one round. Depending on partnership agreement, it can be an intricate shape-asking bid, but if a simpler version of DONT is preferred, it can just show support for overcaller's suit and ask him to bid more with extra values.