On a new song from the 'The Twilight Saga: Breaking Dawn – Part 1' soundtrack, Bruno Mars warns that 'It Will Rain' everyday if he loses his baby.

The song is more subdued than we're used to hearing from Mars, but that's appropriate for a song from 'Twilight.' The haunting, downtempo track begins with the singer contemplating the potential loss of a lover:

"If you ever leave me, baby / Leave some morphine at my door / Cause it would take a whole lot of medication / To realize what we used to have, we don't have it anymore."

Those opening lines pretty much match Mars' earlier comments about the song, which he described as a tale about "the darker side of love."

The strings at the end give the song a cinematic edge, but for the most part the tone remains the same throughout, with no peaks or valleys, even as Mars sings desperately, "Cause there'll be no more sunlight if I lose you, baby / There'll be no clear skies if I lose you, baby."

'It Will Rain' is not a major artistic leap forward for Mars, but the mood of the song makes it a good fit for the latest 'Twilight' movie, which opens on Nov. 18. The song is available now on iTunes.

Listen to Bruno Mars, 'It Will Rain'