Group of soldiers also involved in scheme (7)
I believe the answer is:
platoon
'group of soldiers' is the definition.
(type of military subdivision)
'also involved in scheme' is the wordplay.
'also' becomes 'too' (synonyms).
'involved in' is an insertion indicator.
'scheme' becomes 'plan' (synonyms).
'too' put into 'plan' is 'PLATOON'.
(Other definitions for platoon that I've seen before include "Infantry unit" , "Small body of soldiers" , "Sub-unit of a military company" , "Team under lieutenant" , "Subdivision of a company" .)