Bruce, Christopher, Brett and Peggy in the grounds? (4)
I believe the answer is:
'grounds?' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for lees that I've seen before include "Wine at bottom of glass" , "Sediment from wine or beer production" , "Sediment that settles at the bottom of liquid" , "Sediment that settles at the bottom of wine" , "Wine dregs" .)