The Blue Club system uses the 2D opening to show any 4-4-4-1 hand with 17-24 hcp.

Responses:

2S is an attempted signoff;

2N shows any bad six card suit; and

3 of a suit shows a good six carder (headed by at least AJ).

2H is used an inquiry;

the rebids are:

2D - 2H; 2S 17-20, either major singleton

2N 17-20, club singleton

3C 17-20, diamond singleton

3D/3H/3S/3N 21-24, singleton in next suit (3N = clubs)

After the inquiry, responder can signoff at any time except in the relay suit (opener's short suit, except 2N over 2D-2H; 2S is considered the relay).

For 17-20 hands, (except for the 2D-2H; 2S auction... see below) The first relay ask asks for the range:

first step 17-18 second step 19-20

The second relay asks for controls

first step 3 second step 4 third step 5, etc.

The third relay asks for the number of queens:

first step 0 second step 1 third step 2

For 21-24 hands, The first relay asks for the number of controls

first step 5 second step 6 third step 7, etc

The second relay asks for the number of queens.

Over the 2S re-bid, 2N is used as a further inquiry:

2D - 2H; 2S - 2N; 3C 17-20, heart singleton.

3H is used as a further inquiry into the strength:

3S (17-28), 3N (19-20). 3D 17-18, spade singleton 3H 19-20, spade singleton