Is 25a Harrier - Runner more likely to stay the course if given new heart h?r?i??. Just can't see it and if it is, is 23d tired t?r?d Missing final bits of horror movie once, went to bed exhausted
Might be a tad confusing,
I think Harrier is the answer.
(If you were to change its heart(middle letter)you could get Hardier (more likely to stay the course))