You were kidnapped by terrorists and brought to a castle far away from the civilization. They force you to construct a nuclear bomb for their next big attack so it's your job to escape the castle.
Mario is going to war with Bowser on the sea. Defense your castle against Bowser invasion. Send Bowser home using you super smart bomb to sink Browser navy.
Shoot, upgrade, conquer enemies, defeat bosses, acquire achievements, collect gems, all in an attempt to save yourself and your gun from the clutches of the evil Professor.
