1979. Nick Storey is transferred to head up a new internal investigations unit required by Mrs Thatcher's new government. His unit uncovers several illegalities including thefts of Government property and a false travel expense claim by an official who subsequently kills himself. Nick is alerted to a massive undercover operation which appears to be both leaking large sums of VAT revenue and also involving illegal action by investigators. When he raises this, he finds most of the Board, from the Chairman down, lined up against him. As the operation goes belly-up, his opponents become nastier and it takes some quick thinking by Nick's team, and Rosemary putting her life in danger, before the case can be resolved. And even then, there are stings in the tail. "On a carousel" is the fifteenth book in a series of detective stores set in HM Customs & Excise, by Richard Hernaman Allen, a former Commissioner.