The Red Room by William le Queux

One fact was quite plain. It was the false Professor who had written to my wife. For aught I knew, the man whom I had followed from Edinburgh to Glasgow might have already been in London, and she might have met him by appointment.

During the morning I took the "forty-eight," and ran over to Regent's Park, passing slowly before both front and back of the house in Sussex Place. The blinds were up, but from the condition of the doorsteps it was plain that the place was tenantless.