More than ever, Clint Eastwood's acting is all squint, rasp, sinew, and bone, but damned if he doesn't have a few tricks left in him. Blood Work, in which he's cast as a retired FBI agent who goes back on the beat, with no legal authority, to face down a serial killer, is a sturdy, if dawdling, old-fashioned adding-up-the-clues mystery that turns out to be one or two notches cleverer than you expect; it's tasty and diverting genre popcorn.
Eastwood's retired enforcer gets back in the game as a solo investigator despite the fact that he's recently received a heart transplant. (His cardiologist, played with whip-tongued feistiness by Anjelica Huston, keeps chewing him out.) The medical gimmick supplies him with motivation -- the ticker he's carrying around in his chest turns out to have a connection to the killer -- but the canniest aspect of ''Blood Work'' is the way that it makes the issue of Eastwood's age (he's 72) genuinely dramatic. It's not just that, like John Wayne in ''McQ,'' he has given himself an excuse for cutting down on the action scenes. He's now playing a man whose will is stronger than his body, and it's that tension -- between anger and frailty, steel and decay -- that powers the movie.
We see the killer, in his ski mask, on surveillance videotapes taken at a convenience store and at an ATM. He also leaves clues for Clint in the form of Manson-style blood-scrawled messages. The villains in Eastwood thrillers always seem to be obsessed with him, but then, so is everyone else in ''Blood Work,'' from the cops and cronies he has to manipulate for information to the goofy loser on the neighboring fishing boat, played by a floppy-haired, lank-grinned Jeff Daniels, who springs a few wily image-retooling tricks of his own.