Transfixed (7)
(Other definitions for riveted that I've seen before include "Completely engrossed" , "Immovably fixed" , "Rendered motionless by concentration" , "Held firmly" , "Fixed (as attention may be)" .)
'transfixed' is the definition.
('impale' can be a synonym of 'transfix')
This is the entire clue.
(Other definitions for impaled that I've seen before include "Stuck" , "killed for a vampire" , "Pierced as with a stick or stake" , "Pierced through in mid-leap" , "Transfixed" .)