Ten falling into trap immediately after (4)
I believe the answer is:
next
'immediately after' is the definition.
(I've seen this before)
'ten falling into trap' is the wordplay.
'ten' becomes 'X' (Roman numeral).
'falling into' indicates putting letters inside.
'trap' becomes 'net' (net is a type of trap).
'x' inserted into 'net' is 'NEXT'.
(Other definitions for next that I've seen before include "Immediately afterwards" , "The one following or adjacent" , "Nearest in space or position" , "Soonest encountered" , "Closest" .)