“I feel like the substance has been draining from me,” says Mac (Sango Tajima). “I feel like I’m transparent now, or like a gentle wind could come along and just — poof! I’m gone.”

Little by little, she’s stripping away her defenses in “Monument, or Four Sisters (A Sloth Play)” to tell her sisters, and the audience, what really happened when she left the job she loved. It takes a trip by car, various boats and a small plane to a remote island where there’s special coral for Amy (Erin Mei-Ling Stuart) to study, but the story starts to come out piecemeal, in little oblique, tightly held bits.

But if Mac’s line is lovely, it also unfortunately describes the play in which she appears.

Sam Chanse’s script, whose world premiere opened Saturday, May 14, atMagic Theatre,collects a bunch of finely etched fragments, offers an intriguing peek at each and then tucks each story line away again, or lets it crumble, just as it begins to glimmer. The result is a shambles of good ideas, creatingthe brow-scrunching feeling that you still haven’t gotten to know someone even after you’ve spent a couple of freewheeling hours in their company.

“Monument,” directed by Giovanna Sardelli, follows four sisters each bearing a private grief. The perfect but aloof, unresponsive Lina (Lisa Hori-Garcia) is stuck in a bad marriage. The ambitious Constance (Rinabeth Apostol一百万年社会正义的战斗战斗s the only woman and the only person of color in the writers room for a children’s TV show about sloths. Amy can’t stop thinking about climate change’s destruction of coral reefs and never sees her wife. Mac drifts.

If those griefs rarely intersect — if the sisters more report the past to each other than enlist in and engage with one another’s causes in the present — “Monument” is more successful in its grand theatrical gestures.

The show zips back in time to envision the quartet as little girls, when Constance and Mac wrote epic, mythic scripts for everyone to act out, trying out their imaginations and verve locked away from the scary knocks and stomps of their unseen, angry father. Even more felicitously, the quartet play the sloths of Constance’s TV series, showing how that same childhood imagination has both stayed the same and evolved — buffeted by the prejudices of Constance’s coworkers and industry, but still inspired, after all these years, by her sisters.

It’s a riot to see Sardelli’s cast flip from their restrained, pellucid portrayals of the sisters to their larger-than-life embodiments of the sloths, who when stressed might curl into the fetal position, start climbing a pillar, creep into an embrace or scratch their heads with their awkwardly long toenails. These are exactly the kind of roles that Asian American actresses so rarely get to play, and Tajima and Apostol, in particular, feast on them — Tajima with full-body expression and confidence that could make you think cartoon melodrama had originated in the sloth species, Apostol with a sloth dudebro physicality and intonation that might make you want to cast her in a buddy movie.

In spite of fascinating forays into science and playful bits of staging — animated sequences by Sarah Phykitt that bring out a sense of childhood wonder, a coup de theater in the form of a wildly oversized costume by Brooke Jennings and Michelle Mulholland — the fun frequently trails off, as if the show took the first good idea for how to end a scene and hurriedly ran with it.

The acting, too, can feel unfinished, with one performer still reading lines from a cheat sheet on opening night.

Coral responds to its warming environment, just as the four sisters are still responding to their difficult childhood. “Monument” monitors their responses just as Amy gathers data on the coral. And like uncombed data, “Monument” can be frustratingly withholding — a jumble that doesn’t paint a picture.

L“Monument, or Four Sisters (A Sloth Play)”:Written by Sam Chanse. Directed by Giovanna Sardelli. Through May 29. One hour, 55 minutes. $20-$70. Magic Theatre, Fort Mason, 2 Marina Blvd., Building D, Third Floor, S.F. 415-441-8822.www.magictheatre.org

Editor’s note: A previous version of this story gave incomplete costume design credits. Brooke Jennings designed and built a key costume based on sketches Michelle Mulholland provided.