Chances are if you spot a man (and it is always a man) hunched over an iPad on the morning commute, he'll be playing a tower defence game. To the outside world, this rumpled suit feverishly working his tablet looks like any other worker drone. But in the private world on screen, he's a military genius, marshalling armies across the ruins of a virtual world and Anomaly: Warzone Earth is the stuff of his dreams.

This excellent little game is a conversion of a PC title released last month, and at a mere £2.49 on the iPad it's an absolute steal. In tower defence games every second counts so, in brief, especially for those fingertip Sun Tzus, here's the simple version: in Baghdad, in the future, there's a comet, aliens are involved and, inevitably, conflict – portrayed in an RTS with precise, fluid controls and ingenious graphics. It plays brilliantly and not even a dodgy Jason Statham impersonator doing the voiceover can detract from the fun – unmissable.