Treat cold going in to liaise (8)
I believe the answer is:
medicate
'treat' is the definition.
(medicating is a kind of treating)
'cold going in to liaise' is the wordplay.
'cold' becomes 'c' (eg on taps).
'going in' means one lot of letters goes inside another.
'to liaise' becomes 'mediate' ('mediate' can be a synonym of 'liaise').
'c' put within 'mediate' is 'MEDICATE'.
(Other definitions for medicate that I've seen before include "Give a drug to" , "Supply drugs" , "Administer a drug to" , "Treat (one) with drugs" , "Treat with pills, drugs etc" .)