The Venus Flaw

When Dan and Wendy Griffin find a cave full of prehistoric artwork on the coast of Malta they are plunged into a living nightmare of violence and intrigue.
Someone is clearly trying to keep something hidden, but who? And what?
Unable to trust the police or the British Embassy and with no clues other than the cave itself and the fact that one of the men trying to keep them from it works for the National Security Service, they must try to figure out what is going on before one or both of them are killed.