In “The Lincoln Lawyer,” Mick Haller (Matthew McConaughey, “Ghosts of Girlfriends Past”) skates along with one foot on the ethical side and the other, not so much.

Haller has no office, but operates out of his car’s backseat, hence the title. His clients tend to be on the lowlife side: bikers, hookers, dealers. A few years back, one of them, Jesus Martinez (Michael Peña, “Battle: Los Angeles”), was accused of beating a prostitute to death. So convinced of his guilt was Haller, the lawyer talked the guy into a plea bargain that saved him from the needle, but got him a life sentence.

Now, Haller has a new client, a rich and respectable one in Roulet (Ryan Phillippe, “Macgruber”), who says he was set up in a scam the same way Martinez was. As Haller and his investigator, Frank (William H. Macy, TV’s “Shameless”), look into the situation, it seems both clients could be telling the truth.

The film is based on a novel by Michael Connelly (“Blood Work”), so the plotting is trickier, but makes more sense than the standard-issue movie thriller. The script is by John Romano (“Nights in Rodanthe”), who knows how to pace the twists and action scenes, and direction is from Brad Furman, who doesn’t show signs of developing genius, but this is solid work and he could go on to a future of professionally made cop and crime dramas.

There is nice work from the rest of the cast, none of whom do breakout work, but they certainly won’t embarrass their loved ones, either. Haller’s former wife (Marisa Tomei, “The Wrestler”) works for the authorities and thinks her ex should be pickier when it comes to clients. Val (John Leguizamo, “Gamer”) scrounges for clients in holding cells; Mary (Frances Fisher, “The Roommate”) is the rich kid’s clutch-butt mother; and Earl (Laurence Mason, TV’s “Prison Break”) is Haller’s driver and the voice of street-smart reason.

But the picture belongs to McConaughey, who has an edge to his folksy, good-ol’-boy persona when he wants to use it. He always seems to be re-inventing himself — one minute, he’s doing some dreadful romantic comedy, and then he does something powerful and off-the-wall. You know he’s been around the block more than once, but it still comes as a surprise that he’s been in 30 films in 20 years.

Anyway, he’s good here as a man who decides to find out whether or not he’s got a conscience. The movie isn’t challenging — honestly, it’s got a lot of CBS prime time in it — but Haller is complicated, and the plot springs more than one surprise. It’s not a home run, but it is a solid double.