Their steps died away down the passage and across the stage. A door slammed and the theatre was silent.

‘Come on,’ said Alleyn.

He led the way round the back of Jacko’s set to the prompt corner.

Only the off-stage working lights were alive. The stage itself was almost as shadowy as it was when Martyn first set foot on it. A dust-begrimed lamp above the letter rack cast a yellow light over its surface.

In the centre, conspicuous in its fresh whiteness, was an envelope, that had not been there before.

It was addressed in a spidery hand to Chief Detective-Inspector Alleyn.

He took it from the rack. ‘So he did it this way,’ he said and without another word, led them on to the stage.

Jacko’s twisted stairway rose out of the shadows like a crazy ejaculation. At its base, untenanted chairs faced each other in silent communion. The sofa was in the darkest place of all.

Young Lamprey began to climb the iron steps to the switchboard. The rest used their flashlamps. Five pencils of light interlaced, hovered and met at their tips on a crumpled newspaper. They advanced upon the sofa as if it housed an enemy but when Alleyn lifted the newspaper and the five lights enlarged themselves on Dr Rutherford’s face, it was clearly to be seen that he was dead.

The little group of men stood together in the now fully-lit stage while Alleyn read the letter. It was written on official theatre paper and headed: ‘The Office. 1.45 am.’

Dear Alleyn,

I cry you patience if this letter is but disjointedly patched together. Time presses and I seem to hear the clink of constabular bracelets.