A James The Fourth Man? (5)
I believe the answer is:
blunt
This clue is a double definition.
'a james' is the first definition.
(James Blunt)
'the fourth man?' is the second definition.
(spy Anthony Blunt, aka the fourth man)
(Other definitions for blunt that I've seen before include "not cutting" , "Straightforward" , "Lacking edge; forthright" , "Frank - Soviet spy, d. 1983" , "Plain-spoken - lacking point" .)