Not that anyone really needs any further persuasion, but Blizzard again proves its mastery of CGI with the intro video to StarCraft II’s second episode, Heart Of The Swarm. The Zerg attack a Terran city, their flailing tentacles and purple slime befouling its wide and faintly European neoclassical boulevards. Facing them is the heavy metal of the Terran forces. Marines unload their rifles into the impact craters from the Zerg’s drop pods; Vikings are smashed by the tusks of stampeding Ultralisks. In a vast square, a line of dug-in Siege Tanks shells a tsunami of writhing talons, bone, spines and mucus.It’s the classic Zerg rush, then, and a tableau that more or less follows the action in the game itself, even if you’re not used to seeing it from such dramatic angles. And the Zerg – innumerable in all their oozing, chittering, pulsating and bursting horror – are the focus of this new expansion to StarCraft II. Which raises the question: why on Earth would anyone want to play a whole 20-mission singleplayer campaign as the Zerg? Especially when it follows the down-home grit of the Western-tinged first episode, Wings Of Liberty, which focused on the adventures of Jim Raynor and his gang of rebel Raiders as they faced up to the despotic reign of Emperor Mengsk.Blizzard’s answer is Kerrigan. Once a Terran – which is to say human – and even Raynor’s lover, Mengsk allowed her to be captured and infested by the Zerg all the way back in the original StarCraft. She then became the Queen Of Blades, the powerful psionic leader of the Zerg swarm. At the end of Wings Of Liberty, Raynor mostly restores her humanity, although she has other ideas about her fate. Heart Of The Swarm’s campaign follows her quest to reunite the Zerg swarm, which broke apart after her departure, and exact her revenge on Mengsk.