Is Lassie on vacation saving a good dog? (6)
I believe the answer is:
'dog?' is the definition.
(beagle is a kind of dog)
'is lassie on vacation saving a good' is the wordplay.
'is' becomes 'be'.
'on vacation' says to hollow out the word (remove centre letters).
'saving' means one lot of letters goes inside another.
'good' becomes 'g' (abbreviation).
'lassie' with its centre removed is 'le'.
'bele' going around 'ag' is 'BEAGLE'.
(Other definitions for beagle that I've seen before include "Type of hound" , "Short-haired dog" , "Hunting dog followed on foot" , "hunting animal with smooth coat" , "Small short-legged hound" .)