the punishment is getting him off — "Too they wouldn't have got him…"

The exact inversion of the frame: where present-tense Gately mows "addict" to keep the narcotic out, flashback-Gately has the buzz-uncut Canadian Talwin forced into his vein by people holding him — the recovering addict's worst fear, being got high against his will, made the instrument of punishment. And even here his mind works the pharmacology to reassure itself, reasoning that if they'd meant to kill him they'd have used something cheap, that getting him off means they mean him to live. The disease returns not as temptation but as assault; his sobriety is not a thing he can defend when enough hands hold the syringe.