“Never Let Me Go,” the new Carey Mulligan film about a world where children are cloned and raised to be spare parts for the ailing is the least science fictiony sci fi film ever. There are no spaceships, ray guns or robots anywhere to be seen. Instead it is a beautifully acted, deliberately paced story about the nature of love, loyalty and the cost of life. Based on Kazuo Ishiguro’s 2005 novel of the same name—called the book of the year and the decade by Time magazine—it’s not an easy movie. There are no villains, even though these children are essentially being slaughtered, nor is there much dramatic conflict. In their place are questions, ideas and an intellectually devastating climax. Grounding the movie are three remarkable performances. Carey Mulligan is luminescent as Kathy in a performance so subdued and so beautiful it’s hard to believe she is acting. Keira Knightley digs deep as organ donor Ruth and Spider-Man-to-be Andrew Garfield (also soon to be seen in “The Social Network”) shows some real promise. “Never Let Me Go” is a sophisticated horror film that will stay with you long after you leave the theatre.