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A new serialized novel starts in next month's issue.
Literal
Next-month [possessive-の] issue from new serialized novel [subject-が] begins.
来月号 ('next month's issue') uses 号 as a counter/suffix for numbered issues of magazines or publications. 連載 ('serialization') is a key publishing term — 新連載 = 'new serial.' Japanese manga, novels, and essays all have strong serialization traditions, so this vocabulary is culturally common.