With Optimus Prime searching the cosmos for the Creators, a new alien threat arrives on Earth.

If Optimus Prime, Autobot leader and all-around mensch, really wanted to save humanity, he would have stopped director Michael Bay around four Transformers movies ago.

The quality took a precipitous drop after the strong first live-action film in 2007, and while it’s not as mind-numbingly offensive as the Revenge of the Fallen sequel, the new fifth installment Transformers: The Last Knight (* out of four; rated PG-13; in theaters nationwide now) is an exhausting marathon of complete nonsense. Even if you love alien robots punching each other while tossing out insipid one-liners, it’s a painfully long two and a half hours where the biggest problem isn’t a lack of plot but way too many of them.

In terms of manly manhood, Mark Wahlberg continues to be a cut above original star Shia LaBeouf. A hero of the last film Age of Extinction, Wahlberg’s inventor Cade Yeager is running a junkyard and harboring Autobot fugitives like his bud Bumblebee (who still communicates via random old movie lines) and cigar-chomping Hound (voiced by John Goodman) when the world deems Transformers illegal after all the wanton damage their battles cause. The government, however, has no qualms about partnering with evil Decepticon leader Megatron (Frank Welker), though he’s tried to take over the globe multiple times.

But Decepticons aren’t even one of Cade’s top five issues. After his allies — including feisty Izabella (Isabella Moner) and comic relief Jimmy (Jerrod Carmichael) — are attacked by Megatron’s minions, Cade is inexplicably whisked away to England to partner with haughty history professor Vivian Wembley (Laura Haddock) and oddball lord Sir Edmund Burton (Anthony Hopkins). In rambling fashion, Edmund gives the rundown on how…