For six nights, Mrs Agnes Bell heard three knocks at precisely one o'clock in the morning.

Always three.

Always from the inside of her bedroom door.

Her husband had died the previous winter, and neighbours assumed grief had affected her.

On the seventh night, she asked Cryer to remain in the house.

At one o'clock, three knocks sounded.

Cryer was standing beside the door.

He opened it immediately.

The landing was empty.

The house was silent.

Cryer searched every room and found nothing.

Then came the knocks again.

This time they sounded from behind him.

Three knocks.

From inside the wardrobe.

Cryer opened it.

Nothing.

The following morning he examined the house's timberwork and discovered that a heating pipe ran behind the bedroom wall.

Changes in temperature could have caused movement.

He believed he had found the explanation.

Then Mrs Bell showed him something.

On the inside of the wardrobe door, at shoulder height, were three fresh marks.

They had not been there the previous evening.

Cryer could find no tool marks.

The marks were simply there.

He ordered the wardrobe removed.

Mrs Bell refused.

She continued hearing the knocks for another nine nights.

On the tenth, they stopped.

Cryer never recorded what he believed caused them.