On 9 July 1864, businessman Thomas Briggs walked into carriage 69 on the 9.45 Hackney-bound train.
A few minutes later, two bank clerks entered the carriage - but as they sat down, one of them noticed blood pooled in the seat cushions and smeared on the walls.
But there was no sign of Thomas Briggs.
The only things left in the carriage were his walking stick, his bag - and a hat that, strangely, did not belong to Mr Briggs . . .
'A thrilling book, which reads at times like a good Victorian novel... an utterly compelling did-he-do-it' Sunday Times