Detain them in tower (4)
I believe the answer is:
keep
This clue might be a double definition.
'detain' is the first definition.
(I know that keep is a more specific form of detain)
'tower' is the second definition.
(I've seen this before)
'them in' is the link.
I am not very happy about this link. Some or all of it may belong to one of the definitions.
Can you help me to learn more?
(Other definitions for keep that I've seen before include "Remain" , "Main tower within the walls of a castle" , "Retain possession of" , "Board and lodging" , "Retain; part of castle" .)