The Armchair Detective and the Manor-House Mystery

A missing girl...
The manipulative aristocrat, Marcus Dreadbury.
A local gangster with a drug-dealing problem.
The Manor's locked room, with a dusty handle.
Stables, but with no sign of any horses.
A subterranean stream.
Marcus' madcap father.
And a Manor-House full of surprises.
Trench and Old Tom must somehow make the connection, if they are to succeed at playing find-the-lady...