A return to form is always welcome, and so it is for both Liam Neeson and the hard-boiled cop drama with “A Walk Among the Tombstones.” A throwback to the New York detective movies of the 1970s, “Tombstones” is methodically paced and bruising in its approach. Neeson plays a retired NYPD officer hired by a drug dealer to track down the men who kidnapped his wife, collected a ransom and brutally killed her anyway. This movie doesn’t stop with the cause-effect simplicity of “Taken,” but instead dives into the detective’s own shortcomings while the mystery slowly unfolds. There’s an actual investigation and not just a parade of action scenes for the sake of having action scenes. “A Walk Among the Tombstones” may not be an all-timer, but it’s a very nice surprise and a sturdy cop movie that should hold up better than most of its contemporaries.