She may be just a teenager, but Phoebe Rush is one hell of a writer.

Her 3/4 of a Mass for St. Vivian, which she wrote at age 15, and is now receiving its world premiere from Theatre Alliance, is a thoughtful, riveting meditation on friendship, illness and the kind of philosophical soul-searching that seems so essential when we first begin asking ourselves the tough questions about existence and meaning that we'll wrestle with for the rest of our lives.

The authenticity of the two main characters cannot be merely attributed to the fact that Rush shares their stage of life; the playwright has a brilliant touch in re-creating the meandering thought process that goes along with this phase of intellectual development, and captures the emotions that ensue from the intense, unclassifiable bond that the two main characters share.

When marvelling at the artistic achievement that 3/4 Mass is for a woman of Rush's age, it would be easy to set aside the overall impact of the piece, regardless of who wrote it, or the achievements of this staging itself. This would be a mistake, as neither fall short.

The play centers around two friends, Emily (Marybeth Fritzky), an anal-retentive, goody-two-shoes type, and Vivian (Nora Woolley), the kind of rebellious free-spirit to which Emily would naturally be drawn. The two form a connection that is at times heart-wrenching and dysfunctional, but desperately important to each girl, one who is in need of escape from her chafing upbringing, and the other who is wrestling with a painful secret. Rush spends a bit too much time drawing out the secret's revelation, but once unmasked, the play never descends into a treacly pity-party for Vivian. Rush does a fine job balancing more lyrical passages with casual, breezy dialogue between the two friends.

Woolley brings depth to a character that could otherwise feel like a stock iconoclast; we are drawn to her charisma just as Emily can't look away. At first Fritzky relies a bit too much on lip-biting, naive facial expressions, but she comes into her own by the time Emily and Vivian's relationship turns more antagonistic. Theatre Alliance's production is powerful, delivering its impact in small doses; the theatre darkens to reveal walls covered in writing for one poignant scene, and the rooftop set is more than functional as an all-purpose location for the work.

It'd be easy to say that 3/4 of a Mass for St. Vivian is an impressive accomplishment for a young, promising writer. It's heartening to say that the caveat isn't needed; it's an impressive accomplishment in its own right.

3/4 of a Mass for St. Vivian runs through Septemter 10 at the H Street Playhouse. Tickets are available online.