Boris is back, sending shock waves through the city, spreading panic wherever he stalks and seemingly on an unstoppable path to total domination.
No, we're not talking about London and straw-haired pseudo-buffoon Boris Johnson but New York and extra-terrestrial megalomaniac biker Boris The Animal (Flight of the Conchords' Clement).
He's sprung himself from his lunar prison (with a little help from the stomach-churning killer arachnids that live the palm of his hand) and has travelled back in time to 1969 to re-route the course of history.
This means killing Agent K (Lee Jones), whose youthful younger self thwarted Boris's plans, shot his arm off and placed a protective shield around earth, preventing an attack from Boris's rapacious fellow aliens.
However, Agent J (Smith) is close behind Boris, launching himself back to the 1960s with a terrifying leap off New York's Chrysler Building (during his time continuum freefall he passes suicides from the Wall Street crash).
Joining his 29-year-old buddy (Brolin, delivering an uncanny impression of Jones), the pair have to iron out their differences and track down Boris, which involves an amusing trip to Andy Warhol's Factory and a retro Shea Stadium.
Director Barry Sonnenfeld - in charge of his third MIB movie - plays to the franchise's strengths, fleshing out the fractious relationship between J & K and resisting monster overload yet making their screen time count.
There's some sly humour - the casual racism of 1960s cops gets a wry roasting courtesy of Will Smith in a stolen car - and the alien critters are genuinely gut-churning, particularly a giant fish that's only immobilised when J rips its heart out. Not for anklebiters then.
Brolin provides irony-rich fresh blood, Emma Thompson plays its for laughs as a MIB ball-buster and the heart-stopping climax atop the Apollo 11 Saturn V rocket at its launch pad at Cape Canaveral is a genuinely thrilling spectacle.
It's been ten years...but it's been worth the wait.