Two-over-one is a bidding system in which the direct response to partner’s opener also shows an opener if it is a new suit at the two-level.
Two Clubs over One Diamond, Two Clubs or Two Diamonds over One Heart and Two Clubs, Two Diamonds or Two Hearts over One Spade are the six cases of two-over-one.
When the new suit at the two-level is in competition, is by a passed hand or is a delayed response then it shows ten plus HCP’s and promises a rebid just as in the Standard American bidding system.
The bidding: South, with his 13 HCP’s, opens One Heart, and North replies Two Clubs which is forcing to game or at least to the four-level. South shows Club support, and North cuebids his first round Diamond control. East doubles for a diamond lead. South passes to see if North can redouble confirming first round control.
South then cuebids first round Heart control and North shows first round Spade control.
That is all the cuebidding South needs to hear. He then bids Four Clubs which is 1430 minorwood asking for keycards in the agreed-upon suit, Clubs. A response of Four Diamonds shows one or four keycards and a response of Four Hearts shows zero or three keycards. Four Spades is two keycards without the Club Queen and Four No Trump is two keycards with the Club Queen.
North has three keycards, and South knows two additional things. One of North’s cuebids, likely Diamonds, was a void not an Ace and a grand slam is a good possibility. South bids Four Spades, telling partner they have first round control in every suit, to ask if partner has the Club Queen. The next step up says no and Six Clubs says yes with no outside King. South could bid Seven Clubs but decides to bid the major grand for the extra 70 points.
The Play: The Diamond Jack is led which is ruffed in dummy. Declarer draws trump and claims. His last diamond goes on the long Clubs. Declarer gets +2210 for the major grand. Seven Clubs would be +2140.