Deception and Betrayal

The plot is built on layers of deception: the partners deceive the town for decades, Cotherstone betrays Mallalieu by testifying against him, and characters like Stoner and the Petts scheme for personal gain.

The cut cord evidence suggests a deliberate attempt to frame Harborough, pointing to deception.

Mallalieu deliberately lies about knowing Kitely's identity and manipulates the investigation to frame an innocent man, betraying justice to protect Cotherstone.

The possibility that the cord was deliberately cut from Harborough's coil to frame him.

Cotherstone's feigned ignorance and possible betrayal of his partner Mallalieu are central to Brereton's suspicions.