Pay a visit to 100 - that's the lot (4)
I believe the answer is:
call
'pay a visit' is the definition.
(I've seen this in another clue)
'100 that's the lot' is the wordplay.
'a00' becomes 'c' (Roman numeral).
'that's the lot' becomes 'all' (I've seen this in another clue).
'c'+'all'='CALL'
'to' is the link.
(Other definitions for call that I've seen before include "Be in control" , "Short visit" , "Cry - summon" , "That is enough" , "Ring; name" .)