The Importance of Being Earnest
From Tardis Wiki, the free Doctor Who reference
The Importance of Being Earnest was a romance written by Oscar Wilde in the mid 1890s. It premiered on 14 February 1895 to coincide with St Valentine's Day. The premiere was attended by the Paternoster Gang (PROSE: The Importance of Being Strax) and the Sixth Doctor. (AUDIO: Assassin in the Limelight)
When Kája saw the Fifth Doctor in his Edwardian clothing, she asked him if he was "in earnest". When he replied that he was, she asked him when would the show open. (PROSE: Suspension and Disbelief)
Behind the scenes
Suspension and Disbelief spells the title of the play "The Importance of Being Ernest".