Auberon, the brilliant but troubled Director of the Museum of British History (known as BRIT) is preparing one Midsummer's Day for the opening of the most spectacular exhibition the Museum has ever staged. The centrepiece of the exhibition is Gainsborough's portrait of the beautiful but intriguing Lady St John; not shown in London for a hundred years, the painting shows its subject strikingly attired as Puck. As the day passes the portrait arouses in the minds of the museum staff disquieting questions, rivalries, and strangely deep affections. Tension mounts: will the gala dinner be a success? Can the Museum's Chairman be kept under control? And just what is it that's so peculiar about the portrait?