Three animals in the lead (5)
I believe the answer is:
leash
This clue is a double definition.
'three animals' is the first definition.
(I've seen this before)
'the lead' is the second definition.
('leash' can be a synonym of 'lead')
'in' is the link.
(Other definitions for leash that I've seen before include "Bind" , "Three animals" , "Line for holding dog" , "Restraint, tether" , "Strip for leading, a dog say" .)