That face: mouth slightly agape; skin pale; eyes at once vacant and burning with mysterious torment. Though complicated and distressing issues of marital disunity, personal isolation and the role of the imagination percolated throughout last weekend’s production of Peter Nichols’ “A Day in the Death of Joe Egg,” its greatest strength lay in its foregrounding of the title character’s haunting visage: an ever-present reminder of the play’s sorrowful, questioning, broken heart.

The face belongs to Josephine, also known as Joe Egg (Alexandra San Roman ’11), the severely disabled child of Bri (Ben Smolen ’10) and Sheila (Ali Kimmel ’08). Wheelchair bound and often wracked with spasms, “Joe,” as she is called, requires constant and intensive parental care. This responsibility has deepened already-present fault lines within her parents’ marriage. Bri’s constant need for attention and validation leads him to subconsciously compete with Joe for Sheila’s attention, while Sheila single-mindedly clings to the tenuous hope that Joe will one day recover.

To cope, Bri and Sheila construct an ever-expanding fictional persona for Joe: a starchy old woman whose whims and demands must be met. It sounds a bit odd on the page, but Nichols’ writing portrays this (mostly) self-aware game with a good deal of sympathy, showing an acute understanding of the ways individuals use the imagination to both escape from and transform daily tragedies.

The potential and limits of make-believe and performance play a crucial role in Nichols’ text. Early within the play, Bri and Sheila separately address the audience concerning their feelings toward their fellow marital partner. Nichols soon heightens this fairly standard theatrical gambit by having Bri and Sheila freely acknowledge the audience’s presence to one another, and proceed to outline the birth and early years of their daughter in an extended, stylized performance made up of broadly comic anecdotes. Smolen and Kimmel propel the sequence with comic brio, while never letting the audience forget that the couple’s self-conscious playfulness doubles as poignant ritual: if they play the scenes just right, the ending might finally turn out happy.

Director Jesse Bordwin ’10 nicely negotiates the tension between the superficial mirth and underlying sadness of this extended sequence, highlighting the couple’s eclectically-decorated sitting room as both a living and performing space through striking shifts in lighting and staging (both lighting designer Danica Pantic ’09 and set designer Sarah Gillig ’09 do quietly effective work here). However, neither does he overwhelm the audience with theatrical styling. The focus remains on the couple’s coping with struggles past and present.

It should be noted that Joe does not appear throughout much of the first act, making her time on stage all the more vital. To his credit, Bordwin does not sensationalize Joe’s on-stage presence, placing her prominently within the space and letting the action occur around her. San Roman’s detailed, unsentimental performance as Joe similarly avoids mawkishness or bombast, sketching a wincingly realistic portrayal of a body animated by impulses it barely comprehends.

These strengths help to elide some of the flaws in the play’s second act, when Bri and Sheila are joined by their preening friend Freddie (Ben Vigus ’11), his dismissive wife Pam (Rachel Carpman ’10) and, later, Bri’s overbearing mother, Grace (Emily Ruth Levine ’11). The play develops more conventional dramatic rhythms, and Nichols takes some fairly easy potshots at his supporting characters here. Freddie acts as a particularly transparent straw man for a certain type of liberal self-importance masked as holier-than-thou posturing (he begins many a proclamation with the words, “As a Socialist…”).

More troublingly, Bri makes a decision regarding Joe within this act (not to be spoiled here) that would seem to warrant further moral inquiry than the play is willing to give. For a play that seems to castigate Bri’s self-absorption, having the play’s final moment largely hinge on the intricacies of his personal decisions seems a bit limited.

Still, as Bri and Sheila’s carefully balanced relationship to one another and Joe begin to falter, the cast achieves moments of sharp comedy and pathos. Vigus finds elements of genuine empathy beneath Freddie’s bluster, and Carpman delivers Pam’s monologue reflecting on her queasiness around the physically handicapped with bracing candor. As a well-meaning but suffocating matriarch spreading affection and guilt in equal measures, Levine nails the nuances of a fairly stock character. The mixture of tenderness and disappointment that course through her voice when she wraps a handmade cardigan around Joe’s shoulders makes what could have been a throwaway moment shockingly moving.

Of course, a production of “Joe Egg” relies heavily upon the actors playing Bri and Sheila. Smolen and Kimmel inhabit their complicated characters with increasing confidence as the play progresses, and each performance contains at least one indelible moment. Kimmel invests Sheila’s description of Joe reaching for a colored block with an intensity of feeling that heartbreakingly binds together the character’s indignation and embattled hope. When Bri makes a final decision regarding his future with Sheila, Smolen expertly allows flashes of corrosive self-knowledge to break through Bri’s jokey, defensive exterior.

This is a play that cannot afford to turn Joe into anything less than a concrete human being, lest Bri and Sheila’s actions lack weight and substance. Bordwin thankfully seems to know this, and ends the play reminding the audience of Joe’s constant and unresolved presence. As The Rolling Stone’s “Gimme Shelter” surges in the background (a plea for respite with which the characters seem well acquainted), we see Joe alone on a darkened stage, so distant and yet so present, her face framed in pale blue light. The light slowly fades, but one cannot help but keep the image in their mind, desperately wondering what will become of that face and the parents who gaze upon it with teary, uncertain eyes.