The Woman in Cabin 10: Netflix movie adapts a hit book into something different.

Sometimes the most engaging puzzle a thriller has to offer is deducing the calculations that went into creating it—what a colleague of mine used to refer to as the “plot math.” Ruth Ware’s 2016 novel The Woman in Cabin 10 —now adapted as a film for Netflix by Simon Stone ( The Dig )—became a bestseller by combining a classic Agatha Christie–style manor-house mystery with the mid-2010s trend of unreliable female narrators spawned by Paula Hawkins’ The Girl on the Train .

As a variation on the isolated country house, setting The Woman in Cabin 10 on a cruise ship at sea sounds ingenious—if you’ve forgotten that Christie already did it in Death on the Nile . Making the trip a small luxury cruise keeps the cast of suspects few and glamorous. But in the mid-2010s, all the rage