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.
EP2 The First KeyJan 19, 1998
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.
EP3 The WatchersJan 26, 1998
Lisa and Mark are searching for the second key; when they find it, the Watchers try to kidnap them.
EP4 KidnapFeb 02, 1998
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.
EP5 The Crystal ConnectionFeb 09, 1998
Now having all three keys, George and the twins persuade Professor Waters let them in to see the box.
EP6 The TrapFeb 23, 1998
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.
EP7 The Box is OpenedMar 02, 1998
The gateway to the world of Heritron is now opened. George and the twins escape from the Janus Foundation, but are then betrayed.
EP8 Into the BoxMar 09, 1998
Professor Waters retrieves the Box back from the Watchers' Headquarters, and George goes through the portal to lock the doorway into Heritron forever. The Catchers are waiting for him on the other side.
EP9 BetrayedMar 16, 1998
George is held against his will on Heritron. Anna tells Mark and Lisa that they must rescue him.
EP10 The Final HourMar 23, 1998
The twins find George imprisoned in a crystal cell. They manage to break him free, but can they escape from Heritron and get back home?
The Legend of the lost keys is an educational BBC Look and Read production, which was first aired on BBC Two on 12 January 1998, and has been shown regularly ever since.