How do I solve 18 across in Times Cryptic 29538?

Question

Accepted Answer

18 across reads "Policeman about to go into inner working of old scientist" (10 letters); the answer is COPERNICAS. It's a charade: the answer breaks into parts in clue order, each part clued by a word or short phrase. No indicators needed; watch for standard abbreviations (RA = artist, US = American, IN = at home) and short synonyms. The full step-by-step breakdown is on this page.

Policeman about to go into inner working of old scientist (10)

18A — Policeman about to go into inner working of old scientist (10) — COPERNICAS