Don't let the creeps complete their path. Do that by building defense towers along the way. Manage and upgrade them to get to higher levels. You have 6 types of towers to choose from once you have enough gold.
Build lasers, artillery, missiles, slow fields, shock generators and blade launchers to stop wave after wave of creeps, now with 4 maps, and 5 difficulty levels.
The clockworks are attacking! Use your turrets to knock out approaching clockwork enemies. Don't let them reach the source well before the day ends or the battle is lost.
Choose your antibiotics wisely to fight off the infections and save your patient. A fun way to relax and without you knowing it, you'll maybe even learn something useful.
