Lock & Key

Lock & Key is a tower defense game. With only one attacker wave. And it's in text.

The premise is that you're a dungeon designer, the one who lays out the arrangement of traps to keep in the extra-specially-dangerous prisoners. You've got a grid of rooms in which you can place these traps, and a limited budget to spend. When you're done, you're taken aside to a guard room with the King to watch as Boldo -- a kind of Tarzan figure gleaming with oiled muscles -- does his best to break out. If he fails, you win. If not, you get to watch Boldo defeating all the traps you so carefully laid out -- and the consequences for you are disastrous. Time to play again.

While the constraints and challenges are theoretically similar to the ones you'll find in traditional tower defense games, the feel is entirely different. Each kind of trap can be placed only once, and the sequence matters. There's a graphical component to the interface, so that you have some visual feedback when laying out the dungeon, but most of the interaction is through text commands, because Lock & Key is primarily a text adventure in form. And much of the game's entertainment value comes not from figuring out where to place traps -- though that makes a solid and rewarding puzzle -- but from the characters and their reactions. Traps have to be bought from trap-manufacturers, all amusingly characterized by author Adam Cadre (also known for a number of more traditional works of interactive fiction and for a novel, Ready Okay!). And watching the breakout attempt is also a lot of fun. The typical
attacker wave during a tower defense game doesn't make irritated
comments about the traps -- or deftly disable them while you watch in humiliation.

Lock & Key comes with a complete package for play on
Windows; for other platforms, you will need to download the game file and a separate interpreter. The same interpreter will play a wide range of other interactive fiction, however.

Lock & Key won three XYZZY awards, including Best Puzzle of 2002. And if you enjoy its peculiar blend of traditional game premise with off-beat social comedy, you should also try Textfire Golf, by the same author: it's a game of Machiavellian office politics, seen through the medium of sports simulation. Choose your clubs wisely.