2002: the year of the Golden Jubilee, and everyone at Dudley Goring Comprehensive School is in a state of eager anticipation about the arrival of a very important visitor. Her Majesty the Queen is due to open the new Science block.
Everyone, that is, apart from Derek Jones, the school’s Head of Science, an unreconstructed socialist and staunch republican. In a moment of madness, Derek decides to use the temporary 'facilities' – a Portaloo which has been specially installed for the Queen’s own personal use. His timing is, as ever, terrible and he is caught in the act by the Queen herself.
Embarrassment quickly turns to confusion and then fear as they realise they’ve been locked in the Portaloo by terrorists who have planted a bomb underneath, and any attempt to escape will set it off. With no way to contact the outside world, Derek and Her Majesty are forced to rely on each other as they wait anxiously to discover their fate. But will they find some common ground before it’s too late?