How do I solve 21 across in Daily Telegraph Cryptic 31244?

Question

Accepted Answer

21 across reads "Convict's first time in prison" (4 letters); the answer is CAGE. 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.

Convict's first time in prison (4)

21A — Convict's first time in prison (4) — CAGE