As a screenwriter, Shane Black has built a reputation on action movies featuring mismatched partners (Lethal Weapon, The Last Boy Scout). Making his directorial debut, he's chosen . . . an action movie about mismatched partners, played by notoriously insane actors Robert Downey Jr. and Val Kilmer. It's a perfect fit. Downey plays small-time hood Harry Lockhart, who's mistaken for a great method actor and brought to Los Angeles for a big-time screen test; Kilmer plays gay private detective Perry Van Shrike, who has to teach Harry how to act like a real investigator. It probably won't surprise anyone to learn that the two become involved in a very dangerous case that ends up threatening their lives, and trade witty banter while trying to beat the bad guys. But Black knows the formula well, and, via Downey's narration, he lets you know that he knows it, subverting things every once in a while just for a laugh. The zingers come so fast and furious that if you miss a few, there are always more.