Bruce, Fergal, and Stevie are hoping to relax at Tammybrae House in the Cairngorms with Bruce's inventor uncle, Clovis the mackerel cat. They arrive to find that Clovis's latest invention has been stolen, a visiting professor is missing, and a strange yodelling marmot is in charge of the house. Fergal is immediately suspicious. So he persuades the unwilling Bruce to help capture the marmot, who he is convinced must be part of the merciless McKitten Gang, a notorious band of Scottish wildcats who are terrorising the locals. An undercover marmalade cat and a sweet-looking widow with a nasty surprise for the gang leader come to the rescue, with the help of Henrik the hyena detective. Stevie and Max Rump set off to find the professor, but are soon sniffed out by the gigantic Snow Beast Terror. There is nowhere safe to hide. Can anyone or anything combat the invincible monster?