It is drawing near to the end of term & the University at Cambridge is in turmoil over the opening of a new Common Library. There is an attack on one of the masters at a meeting to discuss the matter & a body is found floating in the pond in the library's garden on the eve of its opening. Meanwhile there are rumours of a large force of dangerous smugglers lurking in the Fens. Aided by their friend Sheriff Tulyet Bartholomew & Michael must thwart the invaders before the Feast of Corpus Christi the following week. To fail might mean the destruction of the town...