BR 5MT 4-6-0 No 73109 with an Evening Citizen TV show train returning to Glasgow Queen Street between Whitemoss and Auchterarder in the early evening. A similar shot of 73146 appeared in CJA's 'British Express Trains No.5', in 1957.
There were a number of these day excursions, one of which was to Arbroath on Tuesday July 23rd 1957 (returning at 7.10pm) and it is probably this. There was also one to St Andrews on Saturday 20th but I doubt if it was routed via Auchterarder.

Photo: W.J. Verden Anderson / Rail Archive Stephenson