The detective glanced at the keys--then, suddenly, his revolver glittered in his other hand.
The Doctor watched him anxiously.

A puff of wind rattled the panes of the French windows.

The storm, quieted for a while, was gathering its strength for a fresh unleashing of its dogs of thunder.
The detective stepped to the terrace door, opened it, and then quietly proceeded to try the Doctor's keys in the lock.

Thus located he was out of visual range, and Wells took advantage of it at once.

He moved swiftly toward the fireplace, extracting the missing piece of blue-print from an inside pocket as he did so.