its worth pointing out that this route is due to weekend engineering works (not sure if you are aware) and this service normally goes via taunton which is faster, however you will be embarking on a rare treat... or is that just me being sad?......i will be out with my camera!

You can also look up your train on the National Rail Enquiries website the click on the "Details" link, and under the train you'll be catching click on "show calling points".

First off, welcome to the forum New2trains. 

As for your query; it would help if you can tell us what time you are planning to leave Plymouth, or if you've already booked a ticket, what service you are booked on.

Generally, direct trains to London are diverted after Exeter St David's calling at Exeter Central, Honiton, Axminster and Yeovil Junction, then rejoining their normal route at Castle Cary, from there services have different calling patterns to Reading. Some omitting Westbury and some calling at Pewsey and/or Newbury.

The last direct train of the day leaving Plymouth at 1942 is scheduled via the diversionary route through Yeovil Junction and another diversionary route after Westbury, through (not calling at) Melksham, then joining the Great Western Main Line calling Chippenham, Swindon, Didcot Parkway, Reading and London Paddington