Lock’s Quest has got the ingredients for a handheld sleeper hit on lockdown: intuitive touch screen controls, twist-filled wartime drama, low-tech but charming 2D graphics and inventive gameplay that takes a formula already scientifically proven to be infectiously addictive and adds twists, surprises and depth to it.

The formula in question is the Defend Your Castle-style game, which you might have already wasted plenty of hours playing in the form of browser-based Flash games, like Desktop Tower Defense or (of course) Defend Your Castle (PixelJunk Monsters on PSN is another example). There are waves of bad guys trying to invade your crib, and you have to erect defenses to fend off their attack or otherwise thin out their ranks until they’re history.

In Lock’s Quest, the evil castle crashers are the Clockworks, a race of machines that have been given life by the sinister magic of the power-hungry Lord Agony. When the Clockworks start banging the war drums, Lock - a plucky young lad who can create buildings out of thin air - ends up in the middle of a huge military conflict. 

The story’s surprisingly mature (for all its kiddie veneer, the plot’s neck-deep in moral gray zones) and keeps the game moving nicely, but Defend Your Castle was never fun because of its plot (since it doesn’t have one). The compelling story’s just the icing on the cake for Lock’s Quest – the battles are where it truly shines. These enemy encounters play out in two distinct phases: Build and Battle.

In Build mode, you get a set amount of time to construct your defenses for the incoming enemy onslaught. You’ll place turrets, reinforce defenses and set up traps near enemy spawn points. You get plenty of options, and with a timer constantly ticking, Build keeps you on your toes as you weigh options and plan ahead. It plays like a light real-time strategy game, fast-paced and fun, but still deep and full of important choices.