The Clue of the New Pin by Edgar Wallace

Tab smiled to himself. He who had investigated so many burglaries had never imagined that he would be favoured by the attention of those midnight adventurers. He went into Rex's room, turned the switch, and had only to take one glance to know that somebody had been very busy indeed in his absence. Under the bed which his companion had occupied were two shallow trunks filled with those of Rex Lander's belongings which he had not taken with him. One of these had been pulled out, placed on the bed, and opened. It had been opened unscientifically with a chisel, which Tab knew was his property, and must have been taken from the tool-box in the kitchen. The lock was wrenched off and the contents of the box scattered on the bed. The other trunk had not been touched. Whether the thief had been successful in his quest Tab did not know, because he was ignorant of the box's contents. He guessed he must have been disappointed, for beyond a quantity of underlinen, more or less in a state of disrepair, a few books and drawing; instruments, and a packet of letters which Tab saw at a glance were from Jesse Trasmere, there was nothing at all valuable in the trunk.

He went to his own room, but none of his things had been touched. And then he began a careful search of the other rooms in the flat. They yielded, however, no clue as to the identity of the mysterious visitor, and Tab got on to the 'phone to Carver and was lucky to find him.