In 22nd-century Zimbabwe, the children of General Matsika – Tendai, Rita and Kuda – escape their sheltered life for an adventure in Harare, and are immediately kidnapped and sent to the plastic mines.
Good beginning--we definitely know we're in the future.
The General hires three mutant detectives, Ear, Eye, and Arm, to find them. The detectives, always one step behind the resourceful children, follow them from the mines to the walled-in, secret village of Resthaven – a protected island of traditional tribal life in the middle of Harare – and on to the subtler dangers of Mrs. Horsepool-Worthington, a snobbish society woman who plans to hold the children for ransom.
You're skipping over a bunch of the unnecessary (for these purposes) details, but I'm not sure the ones you've chosen to share are serving your synopsis.
The detectives and children finally meet at the Mile-High McIlwaine Hotel for a showdown with evil telepaths known as the Masks, who threaten all of Zimbabwe. Sensitive Tendai defeats the Masks, with help from both friends and enemies, and grows into a hero.
If there are going to be evil telepaths, you should have introduced them a little earlier. It sounds like they just materialize in the story for the sake of the ending. And (hold on!) Tendai is the hero? That's not at all clear.
This book has a very involved plot, and while part of the appeal is the adventure, another important part is the humor. A synopsis of this story has the challenging task of conveying adventure without trying to tell about all the adventures, and at least implying the threads of traditional folklore and comedy that run through the text.
This one's intriguing, and I might request a manuscript from it, but it could still use some work.