Garrick Theatre | ★★★✩✩

Toby Marlow and Lucy Moss are the Cambridge-educated brains and songwriting talent behind Six, the hit, award-winning musical with the neat idea of turning Henry VIII’s wives into a girl band with kick-ass songs and outfits.

This then is the duo’s “tricky” second show, which makes a virtue of the gender-fluid identity and the achingly meta premise of being a musical about Marlow and Moss themselves and their struggle to find a subject for the follow-up to their hit.

The action is mostly set in the flat inhabited by Marlow and Moss’s alter egos Oliver and Nancy. The names are one of several decreasingly amusing references to the duo’s favourite musical. Designed by Moi Tran, the somewhat cartoonish feel of the set reflects the show’s playful heart. Yet there is heartache beneath the fun-palace energy of Moss’s production.

Oliver (Jo Foster) and Nancy (Leesa Tulley) are best friends who set out to understand why neither can seem to land a relationship. Getting to the answer takes a whopping two and half hours during which the creators prove themselves to be terrific songwriters, but less adept at the art of book writing.

The evening begins promisingly with the number 8 Dates which skewers the ruthless world of app dating (meeting in a bar is so 1800s) but it peaks early with the actually brilliant number C U Never which dishes out advice on how to keep self-respect while texting potential suiters and being ignored by them.

Led by the excellent Noah Thomas, this song is brimful of complex yet catchy rhythms that blossom into an old-school tap dance that mirrors the clicks of texting. And for a while it seems that a Seinfeld-like show set largely in a flat and which is almost about nothing except platonic friendship, might just fly.

But whereas that TV classic was meticulously plotted, this show drifts to its conclusion via a couple of overblown songs that may have been conceived as left-field additions (especially the one about a random bee entering the flat) but are actually over-long self-indulgences (especially the song Disco Ball). Tulley and especially the archly witty Foster are good company but like the rest of us their love-life turns out to far less interesting than two and a half hours can bear. The show is a work in progress, or should be.