Plankton is launching an all-out war against the Krusty Krab, and Mr. Krabs needs the player's help defending his restaurant from Plankton's machines. The player starts with 600 pennies and gains 10c every second. These pennies are used to buy weapons to defend the Krusty Krab from Plankton's attack. The player can place purchased towers on six spots around the Krusty Krab, and can replace towers with others if they wish. There are six types of weapons:
Mashed potato launcher: costs 300c and is the basic tower, shooting at a basic speed and doing basic damage
Scalloped potato launcher: costs 600c and shoots faster than the mashed potato launcher
Raw potato launcher: costs 1,000c and does much more damage than the mashed potato launcher
Ketchup cannon: costs 500c and slows down enemies it hits
Mustard cannon: costs 800c and slows down enemies a lot more than the ketchup cannon
Mayonnaise bomb: costs 1,200c and does huge damage to anything it hits, but is a one-use item
There are three rounds to the game, featuring Plankton using bomber planes and tanks to try damage the Krusty Krab. Planes and tanks can be destroyed for extra money, and there are Krabby Patties falling from the sky to replenish health. After a few planes and tanks are destroyed, Plankton will show up in a souped-up plane (round 1), tank (round 2), or robot (round 3) to try and finish off the Krusty Krab himself.
After Plankton and his robot are defeated in the third round, the player wins.