Scientist Bruce Banner's (Bana) quiet life as a brilliant researcher working with cutting edge genetic technology conceals a nearly forgotten and painful past. His ex-girlfriend and equally brilliant fellow researcher, Betty Ross (Connelly), has tired of Bruce’s cordoned off emotional terrain and resigns herself to remaining an interested onlooker to his quiet life. One day a simple oversight leads to an explosive situation and Bruce makes a split-second decision; his heroic impulse saves a life and leaves him apparently unscathed -- his body absorbing a normally deadly dose of gamma radiation.

And yet, something is happening. Vague morning-after effects. Blackouts. Unexpected fallout from the experiment gone awry. Banner begins to feel some kind of a presence within, a stranger who feels familiar, slightly dangerous and yet darkly attractive. All the while, a massive creature -- a rampaging, impossibly strong being who comes to be known as the Hulk -- continues its sporadic appearances, cutting a swath of destruction. The military is engaged, led by Betty's father, General "Thunderbolt" Ross (Elliott), along with rival researcher Glenn Talbot (Lucas), and both personal vendettas and familial ties come into play, heightening the danger and raising the stakes in the escalating emergency.