HarperTrophy, New York, 1996, 1^st thus.  ISBN 0-06-442043-4.  Trade soft cover, 87 pages.  Unread copy with a bit of edge and cover wear; binding tight; interior clean and unmarked with tanned pages; black & white illustrations by George Ulrich.  ‘It’s the discovery of a lifetime!  Brian and Penny can’t believe their luck when they find a woolly mammoth tusk in their own backyard – just in time for the local science fair.  But when their tusk is stolen on the day of the judging, they find themselves in the middle of a mammoth mystery!  Can they solve the mix-up and retrieve the tusk in time to salvage their science project?  The thief is betting they can’t – not in a million mammoth years!’ (from rear wrap)