Possible Clues:

• He will arrive, after all
• One threatened with exclusion from first act that was supposed to be prompter
• Recent convert? That's made clear to me
• Eye one initially appearing during Debussy piece?
• The foreign investigator to be given honour by the Queen — one who needs rescheduling?
• Showing pain to me, clear suffering
• e.g. Banquo at the feast
• Ordered ace Merlot -- one will turn up eventually
• Merlot ace (anag) — a recent arrival
• One who’s behind time fixing metal core