Creatures that are party to a terrible crime (7)
I believe the answer is:
Here is my best explanation:
'creatures' is the definition.
(dormouse is a kind of creature)
'are party to a terrible crime' is the wordplay.
'are party' becomes 'do'.
'to a terrible' indicates anagramming the letters.
'crime' with letters rearranged gives 'rmice'.
'that' is the link.
(Other definitions for dormice that I've seen before include "For these heavy sleepers", "Animals", "Bushy-tailed rodents", "Creatures", "They will hibernate", "Little hibernating rodents", "Field rodents", "Rodents", "Furry animals" and "Small field rodents".)