For twenty years, Eleanor and Sebastian Sinclair have built a glittering empire of wealth, philanthropy, and—if the rumours are true—masterful jewel theft. To celebrate their anniversary, the infamous couple boards a luxurious train through the Swiss Alps, planning to renew their vows after a week of extravagant travel. But on the third night, an avalanche brings the train to a sudden halt, plunging the passengers into darkness—and moments later, Eleanor discovers Sebastian brutally murdered in their cabin, a knife buried in his chest. With the train stranded in a deadly snowstorm and nowhere to escape, one question haunts the passengers: who among them is the killer?