This story is taken from the festive anthology release Doctor Who - Blood on Santa's Claw and Other Stories, and was available free to Big Finish Newsletter subscribers in December 2019.
Blood on Santa’s Claw by Alan Terigo
The Doctor, Peri and Joe land on the planet Naxios, where they discover the body of Father Christmas.
Who killed him? The strange individuals dressed in Shakespearian costume or the talking animals wearing waistcoats digging in the tunnels?