The Legend of the Lost Keys

Mark and Lisa need to help their Uncle George (the current guardian) stop an ancient box from being opened. The box is a doorway to a slave world.

George, Mark and Lisa begin the search for the three keys to the box. Lisa is awakened during the night by people who think her uncle has the first key.

Lisa and Mark are searching for the second key; when they find it, the Watchers try to kidnap them.

Having escaped from the attempted kidnap by the Watchers, the twins join up their Uncle George to locate the third and final key at the Roman baths.

Now having all three keys, George and the twins persuade Professor Waters let them in to see the box.

George breaks into the Janus Foundation to try to steal the box back, but then Mark and Lisa realise it is, in fact, a trap.