Hi Wendy
I went to the Cornwall Centre today to look at the St Agnes registers for you.
I found the marriage of of Thomas and Diana:
17 May 1793 Thomas Reynols (Reynolds), and Dianah (Diana) Jorey (Jory)
(Both Thomas and Diana made their mark in the Register).
Witnesses: Richd. Jory, Philip Roberts.
The officiating Minister was Thomas Nankivell, Curate (who was later Clerk of Fowey).
I then found their son's baptism:
Reynolds, Thomas, son of Thomas and Dinah, born 28 August, baptised 28 September 1794.
I then checked the baptisms register from 1793 up to 1803 - no more entries for this couple. (Although there were a James and Elizabeth Reynolds who baptised quite a lot of children in the area! Don't know if there is any connection.)
I then checked the burials from 1794 until 1812 in case either Thomas or Diana/Dinah/Dianah had died, but no record of this. The only burial which may or may not be connected is on 23 February 1795 - A child to Thomas.

I then checked marriages for the same period to see if either had re-married, but nothing.
So... it appears that Thomas and Diana moved away from the Parish. I checked Redruth parish records but they didn't move there. It's a case now of finding where they went.
Sorry there is no additional information as such, except that they moved away from St Agnes at some stage.
Hope this helps a bit. Will have a look at the surrounding areas for records of them as soon as I can.
Kind regards
Bex