Former biker Ki-su (Lee) has now mended his ways and is a motorcycle courier, whizzing packages and people around as necessary. After delivering one package, the building blows up, and at his next pick-up, someone switches out his helmet for an identical model, with a bomb wired to it, which will explode if the helmet is removed, or Ki-su does not obey instructions given to him by an unknown party over a cellphone. Unfortunately, the helment is now being worn by his next passenger, pop singer Chun-shim (Kang), who is supposed to be going to a concert. Instead, she has to be taken along, as Ki-su delivers other explosive packages, and for obvious reasons, becomes the prime suspect in a major police investigation, and matters aren't helped by those who remember him from his wilder youth. It all seems to tie together with some mob dealings, but exactly why was Ki-Su chosen?
There were elements to this I certainly liked: the hero is likeable, the high-concept provides a mechanism to generate some impressive action scenes (there's a fair amount of CGI to enhance them, but the out-takes under the end credits show, that did not entirely remove the risks), and it meshes some fairly disparate elements together well. However, these are countered by some thoroughly irritating aspects, most notably Chun-Shim, who is entirely superfluous to the plot, being little more than a whiny caricature, literally clinging to the hero. It would also have benefited from more focus: while the disparate threads do eventually link up, albeit to varying degrees of satisfaction, it takes its time, and that leaves the viewer circling the plot-lines, able to do little but hope they'll sort themselves out. At 115 minutes, there definitely feels like there's room for tightening; however, it does show that Korea is just as capable as Hollywood, of producing mindless entertainment to pass the time without troubling the brain.