Agent gets tie-up, that's impressive show (7)
I believe the answer is:
'that's impressive show' is the definition.
I can't judge whether this defines the answer.
'agent gets tie-up' is the wordplay.
'agent' becomes 'spy' (spy is a kind of agent).
'gets' means one lot of letters goes inside another (gets can mean captures or absorbs).
'tie up' becomes 'lash' (I've seen this in another clue).
'spy' enclosing 'lash' is 'SPLASHY'.
Can you help me to learn more?
(Other definitions for splashy that I've seen before include "Ostentatious" , "catching crabs?" .)