Gwenda is Matt's aunt and is there when Matt is sent away with Miss Deverill.
Gwenda listens to a man called Rex McKenna on the television, who seems to be hypnotising her. She follows his orders and kills Brian with a kitchen knife, who she realizes treated her badly. She hitch-hikes with a man who drives a petrol tanker, she is told to kill him but decides to knock him out with the blunt side of her axe. Then she drives a petrol tanker into Matt's school in York, which blows the dining area up. If it wasn't for Matt's precognition the whole school would have died in agony. Gwenda's last scene shows her been unsure, rueful and guilty, but Rex persuades her via radio and she reluctantly does it.