“Nocturnal Creatures” arguably marks the climax of the story of Doom Days. The song follows the challenge of facing a grim reality, politically, socially, and otherwise in “Million Reasons” and then the resolution to “take the blue pill” and choose to tune out these problems for a night of partying in “Doom Days.” The song, taking place at 3:28 AM, acts as the partying heart of the album. The chorus in particular represents the voice of all characters involved in Doom Days. There may be subtle hints of lingering self-awareness in the lyrics, such as singing of being “drawn to the flame,” but nevertheless the song’s role is that of an anthem for the party-goers. Dan Smith provided insight into the song’s creation to Billboard:

“Nocturnal Creatures” was kind of the first song that we made that had that breakbeat, ‘90s sound. It was sort of about throwing yourself head-first into the night with somebody and feeling that slightly ridiculous, naive, indestructible feeling, that feeling that you can outwit the sunrise, and it set that nocturnal, nighttime tone for what the album would become.
The chorus is basically everyone that’s found anywhere on the album; we wanted it to be a proper gang vocal.

The song has dark sound but at the same time still manages to maintain an upbeat late-night party feeling. The instrumentation primarily consists of piano sounds with moments of bright synthesizer and touches of guitar. Musically the song may be considered more experimental for Bastille, making noticeable use of drum loops and the repeated line “We’re nocturnal” as a form of instrumentation spread throughout the song. The chorus is marked by a number of backing vocalists, providing the “proper gang vocal” intended.

While sampling was a significant component of Bastille’s previous major album, Wild World, this song features the only spoken sample on Doom Days. The sample, played at the end, is taken from a Highsnobiety video on Russian rave culture following the collapse of the Soviet Union. The sample is included as a way to to sum up the hedonistic worldview expressed in the song and, more broadly, the album as a whole.