This year Christmas will be a bit different for the Keller family: parents Anne and Ben buy their three adult children--Cal, Dylan, and Emory--a river cruise down the Danube River from Germany, through Salzburg, to Vienna, touring beautiful European Christmas Markets and towns along the way. The problem? The very different siblings, each experiencing a personal-life challenge, have naturally gone in separate directions over the years and the idea of spending 10 days cooped up on a river cruise together makes each Keller sibling cringe for their own reasons. But they say "yes" because that's what families do, never expecting it to turn out to be a glorious once-in-a-lifetime experience full of missed connections, new friendships, stunning vistas, relationship upheaval, budding romances, shipboard games, family bonding, and a secret that brings them all together in time for Christmas.