Lock's Quest is a tower-defense game wrapped in some fairly standard RPG elements to give the game a much better plot than a lot of other titles in this genre.
As Lock, you will play a young boy raised in a small village that is suddenly under the threat of an evil that the world thought was gone for many years. With the knowledge that his grandfather taught Lock, he will have to build defenses, set traps, create mechanized fighters of his own, and even get up-close-and-physical in order to defeat the waves of the Clockwork Army that have started terrorizing the countryside.
As the story unfolds, Lock will travel around the land setting up defenses at various battlegrounds. At each location, you have time to spend the in-game currency, Source, on turrets, walls, traps and other devices in order to repel the wave of enemies preparing to bear down on the area. After the wave is complete, you will have some time to repair existing fortifications or build new ones depending on how much Source you have left, or how much you acquired in the previous round's melee.
Of course, Lock doesn't just sit idly by while the Clockwork Army attacks. He is on the battlefield, and while he can deal out some damage, you will have to split his time between weakening the foes by hand and repairing the walls and turrets that are under siege, and it takes a fine balancing of these two priorities to make it through each wave intact.
