High adventure in a time-change fantasy set in Edinburgh, with wonderful--but un-integrated--elements. Simon and Malcolm, visiting their great-uncle Henry, are drawn into an age-old struggle for possession of the contents of the Martlet Box. As youngsters, Henry and the boys' grandmother had time-slipped into old Edinburgh, bringing the box back with them to the 20th century. But misunderstanding the gravity of their mission, they failed to deliver it untouched to Mistress Clarke, emissary of the forces of light. Now the task falls to Simon and Malcolm, who must keep the box's powerful substance from the evil Captain. They do win through, in a breakneck finale involving time-changing, Knights of Light, devils, bats, the ship Nostradamus, and even a philosophical search for the true self. Unfortunately, shallow, inconsistent characterization, a confusing plot, and uneven pacing spoil their victory for reader.