Intrudes in health resort, breaking locks (10)
I believe the answer is:
trespasses
'intrudes' is the definition.
('trespass' can be a synonym of 'intrude')
'health resort breaking locks' is the wordplay.
'health resort' becomes 'spa' (I've seen this before).
'breaking' means one lot of letters goes inside another.
'locks' becomes 'tresses' (I've seen this before).
'spa' put into 'tresses' is 'TRESPASSES'.
'in' is the link.
(Other definitions for trespasses that I've seen before include "Forgive them" , "may they be forgiven!" , "Unlawfully enters" .)