Be effusive when taking us in (4)
I believe the answer is:
gush
'be effusive' is the definition.
(I've seen this before)
'taking us in' is the wordplay.
'taking' becomes 'gh' (I am not sure about this - if you are sure you should believe this answer much more).
'in' means one lot of letters goes inside another.
'gh' going around 'us' is 'GUSH'.
'when' acts as a link.
Can you help me to learn more?
(Other definitions for gush that I've seen before include "Sudden stream or jet" , "Spout powerfully" , "Spout like geyser" , "Speak effusively" , "Be over-effusive" .)