The Mummy, The Will And The Crypt by John Bellairs

A chess set, an old tea-shop sign, a Greek newspaper. . .

The clues to the hiding place of old Mr Glomus's will are as intriguing as they are weird. Johnny Dixon can't resist the challenge to solve the mystery -- especially as he desperately needs the reward money.

But Johnny find himself in deep trouble, for the trail leads to the eerie ruins of the decaying Glomus estate, and to an encounter with a terrifying supernatural evil. Deep in the mansion's subterranean tunnels, Johnny suddenly realises that he is not alone. . .