...
The unknown man standing outside the door pressed his head against it and heard Isabel Smith's footsteps near the doorstep suddenly speed away. His hand gripping the dagger handle tightened fiercely before releasing slightly. He then pulled his hand out of his chest pocket and fetched a long, sharp metal object that he inserted into the keyhole of Isabel's door.
The hard metal slowly twisted around inside the lock, hooking the latch. The stranger applied a little force, and a click indicated that the door was unlocked.
A second before the door lock was completely opened, suddenly there was a "ding-dong" sound from the elevator behind the stranger, and the dim corridor instantly became brightly lit.
The unknown man's body stiffened, and he quickly pulled the metal object out, pretending to be a passerby, rushing towards the elevator.
The elevator door opened in time for Percy Stanton to walk out hurriedly. The unknown man moved to the side and entered the elevator.