Mystery of Metru Nui

The city of Metru Nui is divided into six parts. Each part has a guardian -- a Toa -- who watches over the Matoran who live there. However, something strange is happening: Matoran are vanishing and a mysterious plant is destroying the city piece by piece. The Toa have to stop the disappearances and find a way to save their city. Do they have the skills to solve this mystery? Or will they finally meet their match?