"I'm not alone anymore": Lady Gaga & Joaquin Phoenix waltz, commit mayhem in 'Joker: Folie à Deux' trailer

The trailer for Lady Gaga's new movie, Joker: Folie à Deux, has arrived, and it combines violence, explosions and ... ballroom dancing?

The trailer is set to a rendition of the Burt Bacharach/Hal David song "What the World Needs Now Is Love." First we see Joaquin Phoenix's Joker aka Arthur Fleck in prison, where he meets Lady Gaga's Harleen Quinzel, soon to become his partner in crime, Harley Quinn.

"I'm nobody," a bedraggled-looking Harleen tells him. "I haven't done anything with my life like you have."

We then see Joker in full makeup onstage, clutching a microphone, while Harleen and Fleck seem to watch from the audience. "Let's get outta here," she whispers to him. Suddenly, she's in full glam, waltzing with Joker, intercut with footage of her wearing her normal clothes, waltzing with Fleck in traffic.

Next is a montage of Gaga and Phoenix as Harleen and Fleck, and also as Joker and Harley. Someone asks Fleck, "Tell us, what's changed, Arthur?"

"I'll tell you what's changed," Fleck replies. "I'm not alone anymore."

Cue kissing, more waltzing, Joker beating some guy with a chair, explosions, vandalism, fires, guns, blood and Fleck laughing maniacally while standing in the rain.

The clip closes with Harleen seated across from Fleck, a plastic prison barrier between them. She draws red lips on the barrier with lipstick and says, "I wanna see the real you." He lines up his lips with the lipstick, until he looks like Joker — and then flashes an evil grin.

According to Variety, director Todd Phillips says the film isn't exactly a musical, though it will feature song and dance, and music will be "an essential element." The film arrives October 4.