“You look tired.”

“You should take a nap.”

“You look like crap.”

Throughout “Blood Work,” the crime investigator played by Clint Eastwood is constantly being told how old, ill and out-of-shape he appears. Just as the star’s revisionist western “Unforgiven” depicted what might become of his Man With No Name gunfighter, this movie traces the natural evolution of what would happen to Dirty Harry once he achieved AARP age.

In this enthralling though flawed police procedural, Eastwood plays Terry McCaleb, an FBI profiler on the trail of “The Code Killer.” After arriving at another multiple murder scene where the digits 903-472-568 are left as a clue, McCaleb gives chase to a suspect before collapsing from a heart attack.

Flash forward two years later and McCaleb is the new recipient of a heart transplant. His no-nonsense doctor (Anjelica Huston) advises him to take it easy between his frequent catheter checks and daily allotment of 34 pills. But when Graciella (Wanda De Jesus), the sister of a robbery victim, coaxes McCaleb to help her solve the crime, the former profiler reluctantly agrees. After all, he’s the possessor of her slain sister’s heart.

Constantly battling fever and unable to drive  which compels him to recruit his stoner neighbor Buddy (Jeff Daniels) as a chauffeur/partner  McCaleb begins to uncover seemingly unconnected clues that add up to a killing spree with a profoundly personal motive behind it.

While still fitting comfortably into the standard detective mold, “Blood Work” features one of the more trickier crimes of recent cinema. Oscar-winning screenwriter Brian Helgeland (“L.A. Confidential”) gathers a collection of outwardly random plot strands and expertly fuses them by the film’s end. This is done despite taking great liberties with Michael Connelly’s novel, including changing the identity of the main villain. But even if the revamped perpetrator is easy to spot from the get-go simply on the basis of casting, it’s impossible to guess how and why everything fits together.

Eastwood seems to relish the opportunity to play a man his own age. It’s enjoyable watching the 72-year-old action icon shuffle around, speaking in a labored voice and absent-mindedly rubbing his chest where a giant incision supposedly exists. Eastwood is particularly believable when expressing self-doubt about whether he deserves a heart when much younger patients are still on a waiting list.

Of course, the one area where Eastwood is unwilling to act his age is in a contrived romance with co-star De Jesus, an actress 30-plus years his junior. The pairing is unnecessary  think of the extra strain it could place on his bum ticker  and a little creepy. Their dalliance could have remained a friendship without altering a single plot point.

Otherwise, the filmmaker makes smart choices, coaxing excellent performances from his cast. Daniels brings the requisite loopiness to the role of a guy who lives on a boat, and whose idea of decorating involves the various art that can be fashioned from beer cans. Tina Lifford effectively plays a sheriff who shares some kind of unspoken past with Eastwood’s character. The way they make eye contact and dance around certain words alludes to this but never confirms it.

The only misfire  and it is considerable  resides in the detective played by comedian Paul Rodriguez. Perpetually flippant and antagonistic, Rodriguez exists only to be a thorn in the side of Eastwood. He seems to have no life outside of this role, as if his entire career is based on yelling at his retired foe. Worse, there is no reason given as to why these men have this opposing relationship. Every time the police officer is onscreen it pulls the audience right out of the movie.

For his 23rd directorial endeavor (and 44th starring role), Eastwood opts for a visual style that is as stark and to-the-point as his character. There’s barely a hint of camera trickery or special effects to break up the blandness of the imagery. In some ways it mirrors the approach of most 1970s detective shows, from “Kojak” to “Barnaby Jones,” which allows the viewer to solely focus on the individuals involved. In other respects it’s just plain dull.

Interestingly, as “Blood Work” progresses, the title takes on multiple meanings. It can describe the clinical quality of the investigation, the graphic nature of the crime scenes or the criminal’s hidden intentions. It even can be interpreted as a reference to an underlying familial bond due to the commuted heart.

Or maybe it’s just about some old guy who still needs to have a few tests done at the hospital.