WHAT IT’S ABOUT Earth has been invaded by an alien civilization — apparently a peaceful one — and the invasion force’s leader, Karellen (Charles Dance), wants a human emissary to sell humanity on his aims. He finds that in Ricky Stormgren (Mike Vogel) — a Missouri farmer engaged to Ellie (Daisy Betts). But what does Karellen want? Why is he here? What does he even look like? This three-night miniseries, based on Arthur C. Clarke’s 1953 novel, sets out for some answers.

MY SAY Finally! The adaptation of “Childhood’s End” has arrived. This great white whale of adaptations once defied even Stanley Kubrick, who went on to direct “2001: A Space Odyssey” when he couldn’t secure the rights. The story’s difficult, the themes more so — a stew of philosophy, cosmology, theology and a few other ’ologies.

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Clarke’s vision was utterly counterintuitive to the rest of boilerplate sci fi of the time — the us vs. them, the Triumph of the Human Spirit and so on. This three-parter was written by a highly regarded British TV writer, Matthew Graham, who clearly wants to embrace all that, but also meet the needs of a commercial network halfway.

Does he — it? — succeed? Well, halfway . . . (The first two parts were made available for review); Not too deep, not too shallow, not overly smart, not overly dumb. It’s a goldilocks adaptation (with superior production values) designed to please casual viewers far more than hard-core readers.

But TV’s really about forging emotional bonds between viewers and characters, and that doesn’t happen here. There are too many characters, too many points of view, all subservient to big ideas that don’t even begin to come into focus until late in the second part — just as the unwieldy story starts to go out of focus.

BOTTOM LINE Will everything come together by the third night? Will Clarke’s visionary book make sense? (Or will this turn into total nonsense?) Unknown, but at least there’s enough promise here to hint that it’s worth waiting to find out.