Plucky twins Jennifer and Judy are frustrated when a planned family trip to Switzerland fails to materialize, but their spirits pick up once again when they receive an invitation to join their aunt and uncle on an archaelogical expedition. Soon Jay Squared (as the alliterative duo are called by their father) are travelling with Uncle Philip and Aunt Nona up to Thetford, crossing Norwich and ultimately bound for the northeast coast of Norfolk, to a spot known as Caravan Creek.
Uncle Philip believes that a Saxon ship, still housing many of its artifacts and ornaments, is to be found at this spot, and a little digging rewards the family by producing that very ship. News of the find spreads, and the site is soon plagued by all manner of journalists, historians, and photographers. Not all of the visitors are to be readily trusted, however, and the twins spend some exciting nights unmasking nocturnal figures who are up to no good.
Most shadowy of all is one Professor Mattino, a scholarly rival of the twins’ uncle and a villain willing to do anything to lay hands on the ship’s treasures. When a bag of artifacts is stolen from Judy and Jennifer while they try to hide it in the underground mines of Demons’ Graves, they pursue the professor by car, and attempt “the Sherlock Holmes stunt” to retrieve the stolen goods. Another car chase ensues, while at camp the twins’ relatives contend with fire, threats, and an entrenched shoot-out. After a bumpy ride and a few close calls, the family is reunited once again, leaving Uncle Philip with the glory of discovering the Saxon ship, and giving the team of Jay Squared truly something to write home about. (Take that, Switzerland!)
(Synopsis from www.gladysmitchell.com)