Cloud, the Smiter by Arthur Gask

The inspector came up the pathway walking briskly. He looked solid and convincing as if it were his sole mission in life to be just the ordinary uninteresting member of the force. He appeared to be just a part of a machine, a regulator of traffic, or at best a disturber of the peace of the very minor offenders of the law. Not the man anyone would think to be trusted with the handling of a great and important case. He looked too heavy, altogether too much the embodiment of stereotyped procedure and conventional ideas.

Martin, from the security of the fly-proof wire door, watched the inspector critically and analytically every foot of the way. He took in everything about him, but it was the expression of his face he searched out most.