Iron Man Vol 1 #321

Three recent murders having taken place in Avengers Mansion, Tony Stark and Hank Pym attempt to breach the mysterious door in the basement that the killer was seen to escape through. Their efforts are unsuccessful. They are unaware that Marianne Rodgers is hiding upstairs in the supposedly evacuated building. They call it quits, and Stark says he'll go through the security footage later.

Meanwhile Suzi Endo's arrival at Los Angeles International Airport is secretly observed by Cybermancer. Stark calls Moonraker at Force Works to set up a meeting, then calls the Avengers, currently based at the Wasp's estate. He updates Hercules about the door. Hercules mentions being warned about something by a mystery blonde woman, and Stark is shaken by the possibility it is the blonde he saw during his recent blackout. Stark abruptly ends the call.

Stark reviews security footage and discovers that he's the killer, and as he freaks out he suffers another blackout. He comes to in Hank's room, next to Hank's recently murdered body, and moments later is attacked by Marianne Rodgers; she tells him that her developing psychic powers have not been what drove her insane, but rather telepathic contact with the black stain inside him. She chases Stark through the mansion but as she corners him, she is stopped by the interfering Masque. Later, Hanks Pym awakes, unscathed, to find the mansion empty.