Lord Under London - a Nat Frayne mystery

When a methane explosion in the London sewers spews forth a much-mangled body,  Detective Inspector Nat Frayne finds an ancient Hunter watch still tangled in the bones. It identifies the corpse as an aristocrat who disappeared in mysterious circumstances nearly a century ago. Or does it?The find sets off a spectacular round of litigation between branches of the family, to the delight of the press.
Even better, more corpses keep turning up. Freshly killed this time. When his superiors order Frayne to clear up the case at once, there is nothing for it but to leave the light of day once more behind.