An unexamined life may not be worth living, but an examined one can be ruinously expensive. As calculated by Sam, one of the characters undergoing therapy in “The Animal Kingdom,” the quietly galvanizing play by Ruby Thomas, “Dad has literally spent, what, hundreds of thousands just for me to exist.” That this young man has ended up in a clinic despite a cushy life of private tutors, private education and music lessons shows, he wryly notes, that his father made a “really bad investment.”

“The Animal Kingdom” begins with Daniel (Calvin Leon Smith), a soft-spoken psychotherapist, patiently coaxing Sam (Uly Schlesinger) into more-than-monosyllabic conversation. Both are seated in posture-wrecking office chairs in a windowless space no larger than an escape room. Sam, a zoology major who is on hiatus from college, is a bright and observant young man, with a mind for a menagerie of animal facts. He compares his mother and sister to bonobos, whose female alphas “can be pretty aggressive”; his father, on the other hand, is a hippopotamus whose submerged heart beats once every five minutes. Taken together, they form the fractious animal kingdom that gives the play its title.

As part of the treatment program, Daniel summons Sam’s business-minded father (David Cromer), spiritual-doula mother (Tasha Lawrence), and younger sister Sofia (Lily McInerny), to participate in six therapy sessions with the patient. Jack Serio’s direction puts us in thrilling proximity to the actors. Thrilling, but also cortisol-spiking; the sense of being trapped like animals in a zoo is intensified by an obsidian two-way mirror on Wilson Chin’s spartan set.

For much of the play’s 80 minutes, Sam, his therapist and his family sit in a pentagram of chairs and, to Sofia’s growing dismay, pass the time talking about their childhoods, school bullies, their father’s affair, the migration pattern of certain birds — seemingly every topic except the one that precipitated their therapy sessions.