Laughter and frustration, longing and despair, condescension and self-delusion: These are the notes that make up the turbulent symphony of one Russian civil servant’s life. Askentii Poprishchin has spent many dutiful years pushing papers from one side of his desk to the other, mending the big boss’ writing quills, following all the rules that apply to a clerk of the ninth grade in St. Petersburg circa 1830.

But even as we meet the odd, earnest Poprishchin in The Diary of a Madman, his grip is beginning to slip. And over the course of two hours, he will become increasingly unmoored from reality. For the character, it’s tragic; for an audience, it’s a chance to relish the transformative, commanding, passionate work of actor Ken Clement.

Plantation’s Mosaic Theatre has begun its new season with the stage version of an 1835 short story by Nikolai Gogol. Adapted by David Holman, with an assist from Neil Armfield and Oscar winner Geoffrey Rush (the play’s original star), The Diary of a Madman offers a skilled, versatile actor the chance to deliver a bravura performance – which is precisely what Clement does.

Directed by Richard Jay Simon, with lovely supporting work from Betsy Graver as the women (real and imagined) in Poprishchin’s life, Clement forges a path from farce to tragedy, from tight control to the emotional freedom of madness. His Poprishchin is an unremarkable worker bee, a trapped man of extremely modest means who fancies himself meant for better things.

As his mind unravels, those things begin to include the big boss’ beguiling daughter Sophia (Graver) and a much, much higher station in life. In his shabby attic quarters (designer Douglas Grinn strips away some of the plaster from the walls, symbolizing our hero’s disintegration), Poprishchin writes increasingly worrisome diary entries. He imagines, for example, that two dogs are carrying on a love affair, that he can hear them talking, and that love letters from one canine to the other reveal secrets about Sophia and her feelings toward him.

Clement clowns when he should, takes a pratfall, revels in dropping to his knees to give us Poprishchin’s interpretation of his hated, blustering immediate supervisor. Later in the play, he becomes simultaneously regal and pitiful, a sad-sack jester who fancies himself a king.

Simon and his collaborators, including sound designer Matt Corey (who artfully weaves Russian music throughout the play), lighting designer John Hall and costume designer K. Blair Brown, have kicked off Mosaic’s season with a challenging piece. Much of The Diary of a Madman is funny, some of it touching. But that humor builds to a devastating final scene. And it is to that deeper place that Clement has been steering us all along.