Defend an island's precious crystals against swarms of crawling and flying monsters. Use your money to build towers in place of the trees that are planted near the monsters' path. Of course, money doesn't grow on trees, so you have to collect the coins that are dropped by enemies. Occasionally, an enemy will drop a gem when it is killed. Gems can be placed on towers to give them elemental attacks. Each time that you upgrade a tower, an additional gem can be placed on it. In addition to towers, you can place traps to stop enemies. Unlike towers, traps cost mana rather than gold. On your first mission, you will be asked to choose one of three pets, which will assist you throughout the game. Don't forget to spend your skill points between levels.