A peephole in a door:a glance through the Judas in her front door...
If that's not a snapshot of Margo glaring through the judas hole in the door of her padded cell, then the Professor needs to sharpen the intuitive faculties with a sabbatical of his own in Byron Bay.
The door had a judas hole, covered by a small shutter with an enormous lock.
Origin
Mid 19th century: from Judas Iscariot (see Judas1), because of his association with betrayal.
Judas2
/ˈdʒuːdəs /
1An Apostle; full name Judas Iscariot. He betrayed Christ to the Jewish authorities in return for thirty pieces of silver; the Gospels leave his motives uncertain. Overcome with remorse, he later committed suicide.
1.1 (as noun usually a Judas) A person who betrays a friend or comrade:she was called a Judas and a scab...
To his foes, he is a Judas who betrayed loyal friends.
Audrey is in purgatory and Ken is no better than a Judas.
That doesn't make him a Judas - he's quite entitled to move on.