Spies of the Kaiser by William le Queux

"We're going down to Maldon, in Essex," Ray Raymond explained as we drove along in a taxi-cab to Liverpool Street Station late one grey snowy afternoon soon after our return from Norfolk.

He had been away from London for three weeks, and I had no idea of his whereabouts, except that one night he rang me up on the telephone from the Cups Hotel, at Colchester.