Son covered in blood in spiny bush (5)
I believe the answer is:
gorse
'spiny bush' is the definition.
'son covered in blood' is the wordplay.
'son' becomes 's'.
'covered in' is an insertion indicator.
'blood' becomes 'gore' ('gore' can be a synonym of 'blood'**).
's' inserted within 'gore' is 'GORSE'.
'in' is the link.
(Other definitions for gorse that I've seen before include "Moorland shrub" , "Wild evergreen shrub with golden-yellow flowers" , "Spiny yellow-flowered shrub" , "Prickly moorland plant" , "Yellow-flowering shrub" .)