Johnnie To's latest work, PTU (Police Tactical Unit), is a Hong Kong crime thriller that starts out strongly but ends up running out of gas by the midway point.  When a gang leader is murdered under mysterious circumstances, it falls to Sargeant Lo to investigate.  However, in the pursuit of a suspect, Lo loses his service revolver, and this slipup could cost him a pending promotion.  He sets out on a double mission:  to find the killer and his gun.  One intriguing lead occurs at the crime scene:  there, he locates the victim's cell phone, still functioning, with an unknown caller trying desperately to leave the victim a message.  All of this is compounded by the obvious contempt that other investigative branches of the police force have for Lo;  corruptible and clumsy, he's the local equivalent of the Keystone Kops, but he does have enough friends on the force to help him get by.  The problem with PTU lies in its overdependence upon the situational humor engendered by Lo's attitude toward himself and the investigation;  his buffoonery is supposed to act as a clever foil – and cover – for his obvious skill as an investigator.  The problem is that its charming nature has a very limited range;  watching Lo stumble through various leads soon becomes irritating.  The irritation is compounded by a plot line that meanders aimlessly, weighted down by Lo's obsession with saving himself.  Even the payoff – in the form of a truly bloody shootout between rival gangs that lasts over fifteen minutes – is more of an anticlimax.   This is no way to treat a crime thriller.