Armchair Detective On Board the Steam Train Express

Here comes the choo choo train puffing down the track.

All aboard! Tickets please! Trench and Old Tom board the newly-restored Steam Train Express, and soon become engrossed in their mystery on the move, and ponder their fellow passengers What is so odd about the Mildred sisters?

Why did the Sergeant-Major retire so early? And where has that girl, Debsy got to? Can Old Tom make the necessary connections before journey's end?

Now it's going forward, now it's going back