Phoenix ends season with a frothy romantic comedy — but what's in that froth?

In "Miles and Ellie," Don Zolidis draws on his experience as a schoolteacher to set up a bizarre "meet cute" scenario for the young lovers of the title. A couple of 17-year-olds are carrying out a school  assignment to play a married couple negotiating infant care and other woes of early marriage. What could possibly go wrong, right?

High-schoolers Ellie and Miles regard their assigned 'baby.'

The Phoenix Theatre production is in its second week on the Basile Stage, the cozy underground site of the company's more intimate shows, though production values there are full-fledged and departures from realistic style can seem quite at home.

In "Miles and Ellie," home is where the wounded hearts are, a place where Ellie's can be relentlessly tenderized by her older sister's pounding. Ilyana is a brassy, insulting cheerleader whose popularity at school is substantially based on manipulative promiscuity. The insecure and secretly envious Ellie further suffers from the emotional distance of her parents, Bert and Mary, though they are convinced they head a close family  — apart from Bert's extramarital fling of a few years back.

Zolidis concocts from this suffocating environment a first act rich in repartee, some of it accidental, and an abundance of broad, comic self-definition by everyone in the household. Phlegmatic classmate Miles drops himself into the family blender hoping to get through this experiment in empathetic learning without too much trouble. Then the playwright presses the "puree" button and the audience is in for a frothy ride up until intermission.

Bill Simmons directs a cast finely attuned to making two-dimensional characters seem as full-bodied as possible.  Of course, there turns out to be a crucial third dimension to the romantic couple. In Act 2, that emerges with difficulty after a 20-year lapse, following many changes in the lives of the three young people.

Bert and Mary are pretty much the same, just creakier about it. He's a conservative politician bloviating at home to keep in practice in order to make his narrowmindedness seem a matter of principle. Mary is oblivious to anything unpleasant except when she wants to give vent to her fears and prejudices; if she can't own the unpleasantness, she wants no part of it.

The most admirable aspect of Friday's performance was  the solidity of the title couple (Zachariah Stonerock and Lisa Ermel) both as teenagers and as adults approaching 40 with a mix of bitter and merely adequate experience behind them. Miles and Ellie's misunderstanding half a lifetime ago, which was unsurprisingly triggered by sisterly bad blood, requires healing that must extend into the future Miles proposes in the play's last line.

That's the hopeful, practically formulaic conclusion native to this genre, which Zolidis invests with coruscating wit and touches of family absurdity recalling early Edward Albee, with an overlay of relationship maladroitness a la Woody Allen. The playwright tweaks a couple of romantic-comedy cliches, first with a giddy county-fair montage that firms up the Miles-Ellie bond, later with the cinematic blur of the older Ellie running after Miles.

Throughout, Ellie wins our trust by design, as she addresses the audience now and then,  and we are constrained to see matters from her side; except for Miles, the other characters offer few handholds for affection.

Not to mix metaphors — I'll shelve the blender here — but the play's problem is that the second act is inevitably a letdown.  The first act resembles a balloon close to bursting with the air of both nonsense and tension. The second lets the balloon go, and it zips about the room with a sputtering noise until the action lies inert, waiting limply to be picked up for the final tableau of promised reconciliation.

The grown-up family prepares to go out caroling in "Miles and Ellie"

A long dialogue between Ilyana and Ellie, after the sisters' quarrel breaks up the family tradition of Thanksgiving weekend Christmas caroling, felt like eavesdropping on a therapy session of muted hostility. I was surprised to find my interest in both characters — even Ellie —wilting. Trouble is, the scene is necessary, as Ellie has to become clear about the awful mistake she made that led to her breakup with Miles.

The final scene, sweet and slightly predictable, was nevertheless moving, thanks to the unerring rightness of Stonerock and Ermel in both time frames. Carrie Schlatter was dependably abrasive both as the wild, self-centered girl and the pious, self-centered woman that Ilyana becomes. As the parents, Paul Hansen and Jolene Mentink Moffatt command enough variety as comic actors that their characters' verging on caricature never became tedious.

Linda Janosko's set put the middle-class complacency of the home in perspective, with lighting and sound (designed by Laura Glover and Ben Dobler, respectively) shifting smoothly between realism and fantasy — the uneasy bedfellows of Ellie's mental life.