Arrives in secure room at the top (6)
I believe the answer is:
garret
'room at the top' is the definition.
(garret is a top-floor room)
'arrives in secure' is the wordplay.
'arrives' becomes 'arr' (abbreviation used in transport).
'in' indicates putting letters inside.
'secure' becomes 'get' (secure can mean to get or obtain).
'arr' inserted within 'get' is 'GARRET'.
(Other definitions for garret that I've seen before include "Room on the top floor of a house" , "Small top-floor room" , "Attic, home of struggling artist?" , "Kind of attic associated with impoverished artist" , "Cheap top-floor room" .)