Philip befriends Jack and Lucy-Anne at summer school and invites them home to Craggy Tops to meet his sister Dinah. A terrific friendship develops and one day the children head off to explore an old smugglers' tunnel and discover it leads all the way back home to Craggy Tops. When the children are later taken out on a boat trip they soon find themselves on the trail of money launderers in the disused copper mines on the island.
The children and Mrs. Mannering take a trip to a mysterious mountain cottage, which lies close to an old castle. Curious about the ruin, and eager to find a Tawny Owl nesting in it, the children explore the surrounds. When Kiki goes missing Jack is determined to find her and searches the surrounds, but he is alarmed to discover that they are not alone and soon alerts the others to get help.
The four children inadvertently find themselves in a hijacked plane and after a frightening flight they become stranded in an isolated valley. With the weather turning and the threat of sinister men on their trail looking for a long-lost treasure they must work together to find a safe way home.
Bill hires a boat and takes the children out to the serene Penguin Island for some bird watching. He sets out alone to catch some fish for their dinner but is abducted by two ruthless men and becomes caught up in a sinister plot involving looted treasure. Back at the camp the four children grow hungry and impatient for Bill's return, worried that something terrible has happened. As the weather worsens they become desperate and befriend a native named Te Ariki to help them track down their missing friend.
Holidaying in the Black Mountains, the children take off on a relaxing pony ride only to be ambushed by a wolf-like creature. With their tour guide unconscious and their ponies lost in the surrounding mist the children are all alone in the wild. Forced to hunt and forage for food they stumble across the mystery of the Mountain of Kings and must use all their ingenuity and courage to escape from the clutches of evil scientist Dr Grunwald and his incredible inventions.
Bill and Allison ready themselves for a romantic cruise around the Channel Islands to celebrate their honeymoon. But their plans are stifled by a last minute assignment for Bill to follow the trail of arch enemy Slade - who is ruthless in his search for a hidden map to the ancient treasure of Andrea. The children join the honeymooners and soon enough discover the whereabout of the map thrusting them headfirst into an exciting high-stakes race to uncover the treasure.
The family set off to Turkey on a boating holiday and Bill is yet again asked to investigate a suspicious person, Uma, and his sinister link to a stolen quantity of deadly chemicals. Determined not to let this ruin their holiday they enjoy the sights for a time and befriend a mistreated snake charmer's assistant named Oola. But circumstances dramatically change for the worse, and when Bill and Alllison are abducted by Uma and his henchmen, the children find themselves left behind abandoned and alone. Their only option is to follow the river in a decrepit boat towards the Temple of Death to face their adversaries.
One evening whilst Bill guards the future prince of Tauri-Hessia at Craggy Tops, Jack and Philip decide to sneak out after dark and observe the night creatures. Upon Philip's early return the house has been ransacked and he is captured by a group of Madam Tatiosa's evil cohorts who have everyone including the furture prince in their clutches. It is up to Jack to fearlessly track them down, and with the aid of a travelling circus and a new friend Pedro he is able to overcome the odds, rescue his friends and save the day.
Captured by Tel and Ivan, Jack befriends Otto and the two work together to escape and find the treasure before Tel and Ivan do. Meanwhile a panicked Allison fears for her children and Bill plans a rescue mission. But can he put it into effect in time?
The family have arrived in New Zealand. They are met by Bill's friend and colleague - Dennis who needs Bill's help to solve the mystery of a missing agent who was investigating a villain, Perez. Bill's not interested but finds himself involved anyway. Perez has his sidekick, install a tracking device on it and makes plans to insure Bill and the children pose no threat to his nefarious scheme.
Bill and the children arrive on Penguin Island. While Bill goes fishing to secure an evening meal, the children decide to explore, enthralled with the notion of living in the wild. But they don't notice the strange, wild-haired man watching them, Te Ariki, who they soon befriend. Meanwhile, Perez spies on Bill using the tracking device and sends four men to take him prisoner.
Horace Tipperlong arrives at Penguin Island in his little boat to see the penguins. But the children, suspecting he is involved with the disappearance of BiIll, steal his boat and set off to rescue Bill. Allison, having failed to reach Bill on his mobile phone, is getting very concerned and enlists the help of Dennis. But will this be enough to save the day?
The family goes to Germany. Allison is going to paint while Bill works and the children go on a pony trek with Hans. When ponies are frightened away at their camp, Hans rides off in pursuit but is knocked off the horse and lies unconscious. All their supplies were on the ponies so the children must search for food before they starve. But unbeknownst to them, there are greater dangers.
Unaware of the children's plight, Bill proposes marriage to Allison and she accepts. But her happiness is clouded as the children fail to turn up when they should. A search is impossible until morning, the mist is too thick. While wandering in the foothills, the children see Alexai being pursued by dogs. Hans is rescued but is in a coma.
After attempting to rescue Philip from the Mountain, the children try to escape and discover the anti-gravity cavern. Bill and Allison are in their car when the Mountain rumbles. When Bill sees a helicopter landing he decides to interrogate the pilot. The guards have discovered that Philip is not with Alexai and set off the alarm which places the children in enormous danger.
Bill and Allison are going on a cruise around the Channel Islands for their honeymoon. But Sir George orders Bill to drop everything in order to get on the trail of Slade - a villain. Allison is devastated. The children suggest that they go on the cruise with her instead. But when Lucy-Ann buys an Galley ship in a bottle that Slade is looking for, the children find themselves in terrible danger.
Slade arrives on the ship in disguise as a guest called Eppy with his son, Lucas, in an attempt to befriend the children. Lucas gives Jack a belated birthday present. Slade and Igor continue to try and steal the Galley and after the bottle falls to the floor and breaks, Jack discovers an old map in the ship. The children work together to try and discover where the map leads.
The children continue the search to find where the map leads, with Slade and Igor in close pursuit. After getting a message from home, Allison discovers that she has been tricked. Bill arrives at the ship and searches for clues as to the children whereabouts. In a packet of developed film he recognises Slade and quickly realises that the children are in enormous danger.
The family are going on a boating holiday in Turkey. Bill once again gets a phone call from Sir George at the last minute. But this time he is asked to find information on a small-time blundering criminal called Uma. At the hotel in Turkey they meet a boy called Oola, the badly treated assistant of a snake charmer.
After discovering Oola on board, the children invite him to stay. Bill returns with bad news - the holiday is cancelled. But the kids persuade Bill to stay another day so they can explore the sights along the river, the Temple of Dreams and the Temple of Death. The kids are shocked when they discover that the site is ruined and when the guide suddenly abandons them, leaving Jack's PC missing.
Bill and Allison have been kidnapped by Uma. After retreating into a cave, the children realize they are in the Temple of Death. They find the inner tomb of the Temple and discover the Zero One, which could threaten the world. When Uma arrives he is shocked to find the Zero One missing and sends his men after the children.
The children are looking forward to going on holiday with Bill and Allison, but Bill is instructed by Sir George to guard the future prince of Tauri-Hessia. Unknown to Bill, his car has been fitted with a tracking device by a man working for the sinister Madame Tatiosa, the wife of the Prime Minister of Tauri-Hessia, who wishes to kidnap the present king and place the puppet prince on the throne.
After stowing away in the boot of one of the cars with Kiki, Jack is taken to an airfield where he manages to hide in the cargo hold of their helicopter. Meanwhile, Bill and Allison attempt to escape from their bonds. On arrival in Tauri-Hessia, Jack and Kiki are pursued by Jones. The other children are thrown in the dungeon of Borkin Castle. Jack and Kiki makes their way to the Castle to help.
After finding his way to the Castle and discovering the heavy lock on the dungeon door, Jack leaves with the promises the others of returning with help. He returns to the circus to enlist the help of his newfound friend, Pedro. Meanwhile, the King is captured and taken to Borkin Castle. The children have once again found themselves a part of a bigger scheme and thrilling adventure.
