Hires for a song, to get involved in crime (5,2)
I believe the answer is:
signs on
'hires' is the definition.
(signing on is a kind of hiring)
'song to get involved in crime' is the wordplay.
'to get involved' indicates anagramming the letters.
'in' means one lot of letters goes inside another.
'crime' becomes 'sin'.
'song' with letters rearranged gives 'gnso'.
'gnso' placed inside 'sin' is 'SIGNS ON'.
'for a' is the link.
(Other definitions for signs on that I've seen before include "Employs" , "Hires" .)