From the introduction:
No campaign is easy for a Dungeon Master to run but the Rime of the Frostmaiden Companion ("Companion" for short) is devoted to making it easier and more satisfying for you to run. By providing new hooks, variants, flavor text, as well as any referential information for creature statistics or magic items, this supplement should make for a faithful companion to keep at your side.
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The Companion is quite formulaic; every chapter is designed to be easily digestible, whether you're a veteran reader or just diving into it mid-campaign.
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After careful review, the Companion suggests that Targos be the start of the adventure, as it satisfies the themes of an arctic campaign, has a well-balanced quest for low level parties, and also allows the adventurers to complete the Cold-Hearted Killer starter quest without having to bounce around Ten-Towns. Additionally, Lake Monster can be completed while there, leveling them up again.