Looking at the diagrams it's a rather odd service in that it will be run as a 220/221 from Derby departing at 0649 then not calling at Burton-on-Trent but calling at Tamworth, Birmingham New Street, Univerisity, Worcestershire Parkway, Cheltenham Spa, Gloucester, Chepstow, Newport and then Cardiff Central. The train will then from the 0945 departure to Edinburgh which calls at Newport, Chepstow, Gloucester, Cheltenham Spa, Worcestershire Parkway, University then Birmingham New Street where it joins onto the train from Penzance and continues to Edinburgh.
The return service obviously splits from the Plymouth train at Gloucester then just stops at Newport and Cardiff Central. Then the same unit later forms the 21:03 from Cardiff Central to Birmingham New Street which stops at Newport, Gloucester, Cheltenham Spa, Ashchurch for Tewkesbury, Worcestershire Parkway then goes via the Camp Hill Line and terminates at Birmingham New Street.
I know it's to move stock around and to compensate for the lost rolling stock but it will be odd having a Chepstow and University to Edinburgh train. Also it will be the first time (I think) that a Voyager will be regularly serving Ashchurch for Tewkesbury.