A wooden thud bangs behind him.  The knob is being turned from the outside.  Only the depressed button keeps the vile killer from entering.

Stuffing the cell in his pocket, he whips open the medicine cabinet.  All of the shelves are bare.  He opens the cupboard underneath the sink.  That, too, is empty.  Next to the toilet is a plunger.

He grabs it as the door bursts inward.