Figures defending alien beliefs (6)
I believe the answer is:
tenets
'beliefs' is the definition.
('tenet' can be a synonym of 'belief')
'figures defending alien' is the wordplay.
'figures' becomes 'tens' (ten is a number).
'defending' indicates putting letters inside (inserted letters are defended).
'alien' becomes 'et' (extra terrestrial).
'tens' placed around 'et' is 'TENETS'.
(Other definitions for tenets that I've seen before include "Principles of belief" , "Doctrines or dogmas" , "We stand by these" , "Canons and creeds" , "Beliefs or creeds" .)