Anaïs Mitchell’s folk-blues adaptation of the Orpheus and Eurydice myth features two pairs of lovers whose lives intersect in the underworld.

The costumed seven-piece band never leaves the stage during “Hadestown,” and at the top of Act II its members even get a shout-out by name.

Beforehand, the trombonist Brian Drye confines his noisy warm-ups to an alley next to the theater. Inside, the musical director and conductor Liam Robinson checks in on the cast’s vocal health, sometimes conveying a few notes to the band in the basement before they head onto the stage. “Just keeping the screws tight,” he said.

Meanwhile, the Fates are conspiring. “We’re very close, and usually laughing a bunch,” said Kay Trinidad, one-third of the trio, who share a dressing room.

“Don’t tell everyone — we’re usually the last ones to places,” she added. “We try to beat Patrick Page [a Tony nominee who plays Hades]. If Patrick is ahead of us, we’re really late.”