@mattedgar it’s a temporary (I think) diversion where you go from chesterfield down the Erewash valley route and then hoik a sharp right back up to Derby - with a reverse there. So your Chestefield to Derby time is a lot longer than usual…
https://www.realtimetrains.co.uk/service/gb-nr:G59543/2023-06-08/detailed
Still, it still takes too long even when going the more direct route!