When I first began to miss small sums from the safe I thought I might merely have made a mistake about the sums that I had put away.

Finally, I took to counting the money more carefully.
Then I puzzled for a while.

At last, I sent for this man, who is a detective.

He has come and gone so quietly that probably you have not noticed him.

This man has had a hiding place from which he could watch the safe.