Ambassador and son involved in court case (5)
I believe the answer is:
chest
'case' is the definition.
(both are types of container)
'ambassador and son involved in court' is the wordplay.
'ambassador' becomes 'HE' (His or Her Excellency).
'and' means one lot of letters go next to another.
'son' becomes 's' (genealogical abbreviation for son).
'involved in' is an insertion indicator.
'court' becomes 'ct' (abbreviation used in road names).
'he'+'s'='hes'
'hes' placed inside 'ct' is 'CHEST'.
(Other definitions for chest that I've seen before include "Strong box; thorax" , "Trunk or crate" , "Treasure (or heart) container" , "It's enclosed by the ribs" , "Treasure box?" .)