How does the man behind Russia’s most soothing cartoon dog end up with an 18+ horror hit? Leonid Shmelkov’s ‘Restlessness’ strands two travelers in a roadside hotel they can’t escape.

Nepokoy (“Restlessness”), a feature-length art-house animation for adults, is now playing in Russian theaters. That in itself is news: 18+ animation is a real rarity not only in Russia but worldwide. Nepokoy has already become a phenomenon: it’s the highest-grossing Russian animated film for adults, the living legend Yuri Norstein has praised it, and its heroine has been turned into a Dymkovo toy, a traditional Russian painted-clay folk figurine. Nepokoy’s director, Leonid Shmelkov, is known ...