King John (Brian Dykstra) and Queen Eleanor of Aquitaine (Kate Goehring) in Folger Theatre’s “King John.”

Teresa Wood / Folger Theatre

Of all of Shakespeare’s many immortal works, the now-unknown King John was the first to be adapted for the screen, in 1899 no less. This, to put it mildly, is unexpected. Outside of Shakespearean scholarship, the play’s very existence remains all but a well-guarded secret.

If you read King John, as I recently did, it’s easy to understand why it isn’t a household name. With all due respect to the Bard’s genius: King John is a slog on the page. Its story is dense to the point of being impenetrable. Scene after scene is littered with extended speechifying. The biggest plot twists happen offstage.

Why would Folger follow a sensational adaptation of Macbeth with this? Because, it turns out, the company knows a thing or two about bringing Shakespeare to vivid life. This shouldn’t come as a shock. And yet, here I am, knocked on my heels.

Director Aaron Posner transforms a dull tale of royal lineage into a riveting exploration of political legitimacy and personal identity. The achievement here isn’t that Folger reimagined King John to the point of being indistinguishable from its source material. Sure, fat is trimmed and sinew is added. But more than just the bones remain. A confluence of expert direction, fine acting, and stylish stagecraft pumps vitality into staid British history. Folger is on a roll.

The serpentine plot of King John is best summarized in song by the wicked Disney feline Scar: We’re talking kings and successions. The death of Richard the Lionheart leads to the ascension of our title monarch to the British throne. John’s claim to the title is challenged by France and Austria, in conjunction with his sister-in-law Constance. Her son Arthur, they say, is the rightful heir to the crown. Why? Well, it’s complicated. A Wikipedia wormhole (which veers into topics like Robin Hood and the Magna Carta) awaits anyone interested in the Medieval details.

This production brushes aside such complications and, instead, focuses on execution. I don’t mean beheadings (though there is one here), but the visceral presentation of a byzantine work. The set is bare beside a wooden throne, and a crown-like chandelier that hangs askew above the stage. Max Doolittle’s lighting does the heavy lifting, particularly when battles are dramatized in near darkness. Stylized costumes by Sarah Cubbage combine early 20th-century fashion with ‘70s punk: Striped suits and bowler hats are coupled with leather boots and studded belts.

But it’s King John’s cast that boosts an obscure historical play into stirring palace intrigue. Brian Dykstra, our disheveled English king, is always comically frustrated by the machinations working to tear him down. His mother Eleanor (Kate Goehring, built in metal), keeps a chaotic monarchy on track. The remarkable Holly Twyford raises merry hell as Constance, particularly during a show-stopping speech about loss and grief. Megan Graves (a highlight here as in a Woolly Mammoth production) plays a young boy with innocence and aplomb. But it’s Kate Eastwood Norris who owns this spare stage. Her Bastard (unlike her bravura Lady Macbeth in Folger’s previous production) is multi-faceted, kaleidoscopic. She starts as a Chaplin-like scamp, elbowing the audience with witticisms—and ends with a roar.

Folger opens its King John with gratuitous exposition. The actors take the stage and describe their characters’ backgrounds and motivations. They explain, in third-person, what we’re about to see. Consider it a necessary shortcoming, much like a train ambling upward on a rollercoaster. Once we clear the hill, the ride can be exhilarating.

King John runs at Folger Theatre through Dec. 2, tickets $42-$79.