Place for a plain-clothes detective: hospital department event (8)
I believe the answer is:
incident
'event' is the definition.
(incident is a kind of event)
'place for a plain-clothes detective hospital department' is the wordplay.
I cannot really understand how this works, but
'place' could be 'den' (den is a kind of place) and 'den' is found within the answer.
This may be the basis of clue (or it may be nonsense).
(Other definitions for incident that I've seen before include "Distinct event" , "Happening (often of a criminal nature)" , "Episode" , "Event found ten in CID mix-up" , "Cited inn as source of happening" .)