He left Cannon Row Police Station, walked across the road to Scotland Yard, to confer with Whiteside, who had promised to meet him.

He was pursuing independent inquiries and collecting details of evidence regarding the Hertford crime.
Whiteside was not in when Tarling called, and the sergeant on duty in the little office by the main door hurried forward.
"This came for you two hours ago, sir," he said "We thought you were in Hertford." "This" was a letter addressed in pencil, and Mr.Milburgh had made no attempt to disguise his handwriting.

Tarling tore open the envelope and read the contents: "Dear Mr.Tarling," it began.

"I have just read in the _Evening Press_, with the deepest sorrow and despair, the news that my dearly Beloved wife, Catherine Rider, has been foully murdered.

How terrible to think that a few hours ago I was conversing with her assassin, as I believe Sam Stay to be, and had inadvertently given him information as to where Miss Rider was to be found! I beg of you that you will lose no time in saving her from the hands of this cruel madman, who seems to have only one idea, and that to avenge the death of the late Mr.Thornton Lyne.