Let’s get one thing out of the way, right off the bat: Let Valerie Vigoda sing!

Vigoda’s a veteran performing musician as the lyricist of New York band GrooveLily and a musical theater performer many times over. She’s a proven element with strong chops, and she continued to prove it through the lion’s share of the final preview performance of Joe DiPietro’s “Ernest Shackleton Loves Me.” Yet in the first half hour, the most energetic moments of the show’s instrumental score turned her into the quiet person at a loud party. Which would be fine if she were a guest dropping by to say hello: but Vigoda’s the host, a full half of the cast alongside (the well-heard) Wade McCollum.

Chalk it up as a side effect to an otherwise successful experiment. Musical theater is a format that often leans on large ensemble casts and live orchestras, winning over audiences with a show of force. A tight 90-minute show anchored by a cast of two and off-stage keyboard instrumentals accompanied by banjo and electric violin, “Shackleton” defies the rule of strength in numbers to create a no-less grand spectacle.

Kat (Vigoda) is an unsuccessful opera composer saddled with a newborn in a freezing Brooklyn apartment after her “baby daddy” Bruce (McCollum) leaves for the fast life of a touring Journey cover band. Her latest indignity is her termination from a lucrative contract scoring a computer game, leaving her with nothing but an unwatched video blog for her creative outlet. After 36 hours without sleep, she finds herself receiving mysterious online romantic overtures from her only viewer: Antarctic explorer Ernest Shackleton (also McCollum). Shackleton crosses a century and a refrigerator door to be with his lady love, and Kat finds herself acting as official muse on his beleaguered expedition.

DiPietro’s script never attempts to hide the unreality of the cross-time romance, which is part of the show’s charm: the two interact like childhood playmates deep in a game of imagination time. Shackleton is a self-conscious caricature who seems aware of future events in his life and constantly announces his full name with a Dudley Do-Right timbre. Even Kat’s early stock-footage-happy video blogs and Skype chats with Shackleton – filled with bleeps, bloops and catchy sea shanties – resemble a sort of foul-mouthed “Bill Nye the History Guy” spin-off.

It’s positively camp; but it has campy appeal. It’s a radical ’90s remix of a musical worth checking out.