This is the second half of the Disaster at Darkmoor arc, and is probably the last ever UK-created original Marvel Comics story-line we're going to see in quite some time.
Last issue, human-mind-in-robot-body criminal-for-hire "Assassin-8" stole some anti-matter from a top-secret British research facility. Captain America and Captain Britain were both on the scene. Now Captain Britain is desperately trying to stop the explosion, while Captain America chases the villain who is fleeing the scene with the highly-dangerous stolen goods.
The facility is just about to explode, oh no! Fortunately Captain Britain manages just in time to prevent (through unexplained and un-shown means) the explosion at the research facility.
Assassin-8 is just about to escape, oh no! Fortunately Captain Britain arrives just in time to join Captain America and brings down the helicopter (piloted by evil super-scientist Arnim Zola) that has just arrived to pick up Assassin-8 and the anti-matter cannister.
But the cannister has become ruptured, and is just about to explode, oh no! Fortunately Captain Britain flies into space just in time so that it can explode harmlessly.
Meanwhile, Captain America stands around and provides a running commentary on what is going on.
This final story combines all the intellectual challenge of chewing bubble gum with the sophistication of a poop joke. Combined with staid illustrations and facile dialogue, these is a hugely disappointing finale.
This is the way UK Marvel Comics ends. Despite a few bangs, crashes, and explosions - this one really is just a whimper in the grand scheme of Marvel story-telling.