In Olivia Wilde's Don't Worry Darling, the mysterious trailers and posters have provided us an alluring, yet disturbing, glimpse at what's to expect from the actress and director's sophomore feature film. Starring Academy Award nominee Florence Pugh, pop-star-turned-actor Harry Styles, and Chris Pine, the retro aesthetic and exciting cast have hooked fans since the first haunting teaser trailer. With each new promotional addition, the charm and elegance seems to be quickly unraveling, and yet the same crooning lullaby backs each one. According to an interview with Variety, Wilde revealed that singer and songwriter Styles contributed a creepy original song to the film, and that the song is performed by Pugh.

Following her directorial debut with 2019's coming-of-age comedy Booksmart, Wilde presents audiences with a mind-bending psychological thriller that boasts a star-struck cast. Enamored by Pugh's performance in Ari Aster's sunlit horror Midsommar, Wilde knew she wanted the actress to portray her frenzied main character Alice, and was thrilled to be able to cast Styles as Jack, opposite of Pugh following the cancelation of his tour. In a twist of fate, it turns out the musician, who proved his acting capabilities in Christopher Nolan's Dunkirk, was able to flex his musical talent for the film when he noticed the script mentioned "the trigger song" multiple times throughout.

Wilde says she encourages her cast to give creative input on her films, saying that she believes, "Any great actor is also a screenwriter in the process," and adding, "They are responsible for creating the life of the character, so they bring so many ideas." Allowing different perspectives from those intimate with the script can give a fresh take on the story, and with this openness the director prompted Styles to request control over this undeveloped aspect for the film. Wilde says the actor came to her asking what the melody was, and at the time the "trigger song" wasn't fully realized. She gave him the go-ahead to play around with it and says five minutes later he called back with a bit he'd written on the piano.

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Image via Warner Bros.

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In an email to Variety, Styles explained the idea he worked with to create the original song for the film:

"I wanted something that could be both sweet and creepy, entirely dependent on the context. I remember first playing it on the piano, and it had a sort of homemade nursery rhyme feel to it. Applied to the different moments in the film, I think it takes on a couple of different lives — I hope."

The song is featured prominently throughout the film, and the tune can be heard being hummed by Jack's wife Alice. It isn't confirmed in the interview, but it's likely the melancholy bit we hear Pugh singing in each of the teasers and trailers. The song sparked interest when fans noticed it was the actress crooning the adoring lyrics, "Darling, I'm with you all the time..." with Styles humming eerily in the background. Being described as a "trigger song" in the script sounds like the tinkling piano may be a bit more foreboding than a sweet lullaby.

Don't Worry Darling takes place in an idyllic, experimental development, dubbed Victory, in the 1950s, awash with sunny pastels and sparkling pools. A young new couple, Alice (Pugh) and Jack (Styles), find themselves a part of this brand-new community where Jack finds job security and social status among his peers. The name of the game seems to be safety, order, and complacency. As Jack goes off to work each morning we see Alice descending into a maddening spiral of paranoia, losing trust in everyone around her. The glossy veneer is beginning to crack, but it seems no one will listen to Alice until it's too late.

Wilde, Pugh, Styles and Pine are joined in the cast by Kate Berlant (A League of Their Own), Eternals' Gemma Chan, Nick Kroll, Timothy Simons (Candy), Kiki Lane and Dita Von Teese. Don't Worry Darling is in theaters on September 23. You can watch the official trailer below: