Joined the police? (3)
I believe the answer is:
met
I believe this is a double definition.
'joined' is the first definition.
(meeting is a kind of joining)
'police' is the second definition.
(London Metropolitan Police)
'the' acts as a link.
(Other definitions for met that I've seen before include "Encountered by chance or arrangement" , "Encountered, came across" , "Came together, encountered" , "Got together" , "Encountered, came into contact" .)