A musical version adapted by Rowland Leigh, Cole Porter, Robert Katscher [de] and Edwin Gilbert premiered in 1938 under the title You Never Know, but was a critical and box office flop that closed after only 78 performances.

During a European train journey, a nobleman's butler Josef (Paul Lukas) is mistaken for his employer Prince Alfred von Romer (Nils Asther) by a beautiful woman, Marie (Elissa Landi), and he does nothing to disillusion her.

It is shallow and somewhat obvious in spots, but its little intrigue is set forth with admirable cunning by James Whale and others...The audience yesterday afternoon chuckled with glee when the Prince in brass buttons brought in the champagne, doing the butler's duties in a meticulous fashion.

"[3] TV Guide called it a "pleasant comedy given a sparkling look by talented, classy director Whale";[4] while Allmovie wrote, "By Candlelight is chock full of delightfully double-entendre pre-Code dialogue and dextrous directorial touches.

"[5] The Radio Times said "Universal studios' James Whale, the star director of its famous horror cycle, trespasses here on territory more generally associated with Paramount and Ernst Lubitsch.