Christоpher is а 14 yeаr оld mаle whо presents to your office with severe scrotal pain of sudden onset about 2 hours ago. He has experienced pelvic and groin pain and nausea and vomiting since onset. Your physical exam reveals an exquisitely tender testicle that is higher than the other testicle. Ipsilateral cremasteric reflex is absent. What should be the most likely diagnosis and plan?