I was about to say that there is a very useful website (once you get used to it!):
However, I did a quick check on your journey and found that it did not recognise Holywell in Wales for some reason (even if I used the Welsh name Treffynon).
However, do not despair. You are not too far from Chester, so from Chester you can get a train to Hereford and from there a bus to Hay. You should do the journey in about 4 hours as you will need to change trains at Crewe.
On the Traveline-cymru website, use the "plan my journey" link to work out your travel options.
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