Work together in diplomacy, protecting Queen (8)
I believe the answer is:
interact
'work together' is the definition.
(to interact is to connect or work together)
'in diplomacy protecting queen' is the wordplay.
'diplomacy' becomes 'tact' (tact can mean diplomacy or sensitivity).
'protecting' indicates putting letters inside (inserted letters are held or protected).
'queen' becomes 'ER' (abbreviation for Elizabeth Regina).
'tact' placed around 'er' is 'teract'.
'in'+'teract'='INTERACT'
(Other definitions for interact that I've seen before include "Mix with each other" , "Show effect on each other" , "Can't tire (anag)" , "Affect one another mutually" , "Work reciprocally" .)