When orphaned American Tommy Bassumtyte goes to live with grown-up cousin Thomas at the ancestral Boxleton House in England, the housekeeper disconcertingly welcomes him back with ""It's been four hundred years."" What strikes her is Tommy's close resemblance to the portrait of a 16th-century Small Thomas--and indeed, as Tommy discovers, even the ghost of Small Thomas' grandmother is misled by the likeness. Equipped with a rhyme ("". . . shut in a box/ sealed in a box/ closed in a box. . ."") which he learned from his grandfather who learned it from his, Tommy sets about to find the fabled Bassumtyte treasure, presumably awarded the Catholic underground family by a grateful Mary Queen of Scots. Uncovering boxes within boxes everywhere, Tommy does find in days what the family had missed for centuries: hidden memorabilia establishing Small Thomas as the son, and thus all subsequent Bassumtytes as descendants, of the Catholic Queen. Quite a find, and if it doesn't help pay cousin Thomas' threatened mortgage, a newly discovered painted-over portrait of Mary does that in multiples. Overstretched perhaps, but a nicely appointed old-house mystery.