If you were to mash up the arcade classic Rampart with the action and strategy of Nintendo's Advance Wars series, you just might come up with something like Lock's Quest. This brightly colored action/strategy game plays out in alternating rounds where you first build up your castle and then have to fend off hordes of attackers in a real-time strategy mode. Deceptively simple, Lock's Quest is easy to pick up but promises to be difficult to master.

You play as Lock, an archineer (alchemist engineer) who has the power to convert source energy into physical items. A rebel archineer has discovered how to use source to create living clockwork creatures and is using this mechanical army to attempt a takeover of the kingdom. Fortunately, the clockwork knights are not perfect, and their source expires after two minutes. This is what sets up the alternating play style. During build mode, you use accumulated source to fortify your position before fighting off (and collecting more source) from the clockwork knights during battle mode.

The developers behind Lock's Quest cut their teeth on last year's Drawn to Life, and the experience shows. Lock's Quest is a completely stylus-driven game, with controls that are intuitive and easy to learn. If you know how to drag and drop, you can play this game.

As soon as build mode starts, you have your choice of placing walls and weapons pretty much anywhere on the map. You can also choose to repair items that were previously damaged. Your only real constraints are money and time. Every item that you want to place costs a certain amount of source, and if you can't pay for it, you can't build it. As for the time, well, time waits for no man. As soon as the countdown timer reaches zero, build mode automatically ends, and the game switches to battle mode.

Battle mode showcases a simple but effective combat system. Attacking an opponent requires nothing more than walking up and touching it. Lock automatically paths to any location you indicate on the map, so there's no need for repetitive dragging. Just click on an enemy, and he heads right over. As soon as contact is made, a combat minigame appears. This is determined by your fighting style, which you can switch up at any time. Completing the minigame quickly results in a hit. Make a mistake or take too long, and your opponent will land an attack on Lock.

One combat game consists of nothing more than tapping a series of numbers in order. Another had us dragging sliders across the screen to attack. It may sound simple, but it can be hectic in the middle of a battle. Getting into the thick of things does put Lock at risk, but defeating the clockwork knights nets you more source, which in turn allows you to further fortify your position in the next build round.

Each pair of rounds consists of one day in game time, and Lock spends about five days on each map. As the days progress, the attacks get progressively more difficult, and the enemy AI reacts to your tactics. For example, if the first day's attack comes from the south and you end up using all your resources to fortify the south side of your position, don't be terribly surprised if the next day's attack flanks you from the north. Keeping a consistent defense will require a bit of strategic planning. In all, there are 20 different maps planned for the game, which works out to about 100 days of combat.

One neat trick is the ability to play in a zoomed-out view, which shows more of the map. While some detail is lost, the entire game can be played in this manner, including full combat support. Parts of the game that we didn't get to see include the story mode (though we were assured that a full story line drives the overall quest) and multiplayer. Lock's Quest will support both local and global multiplayer via Nintendo's Wi-Fi connection.

The only real lingering question about Lock's Quest is length. With only 20 maps, there is the potential for somewhat limited replay value. We'd love to see a random map generator included to ensure that gameplay stays fresh every time you start a new quest. Assuming it can hold up under replay, though, Lock's Quest could just end up being another one of those must-have DS titles.