Not Hidden by the Fog — John Creasey

The fog was thick, yellow, sulphurous and impenetrable and just like old times before clean air legislation. Beneath it the villains went about their work quietly and largely undisturbed. Commander George Gideon of Scotland Yard was aware of this and meant to disturb their peace, but before long he found himself involved in a web that was more impenetrable than the fog itself.