We are introduced to the orphans, Jack and Lucy-Ann Trent and their cockatoo, Kiki. Whilst on holiday, they befriend Philip Mannering and his sister, Dinah. Together they explore the uninhabited Island of Gloom, as a dangerous adventure awaits.

The Woods Of Adventure. Jack and Lucy-Ann explore a mysterious castle, but a sinister young man confronts them and kidnaps their beloved pet cockatoo Kiki.

The Valley Of Adventure. Philip, Dinah, Lucy-Ann and Jack find themselves flying straight into a truly amazing adventure on a visit to Scotland.

The family have come to Wellington, New Zealand for a combined holiday and business trip. They are met by Bill’s friend, another agent, called Dennis. Dennis would like Bill’s help to solve the mystery of a missing agent who is investigating the movements of the arch villain, Perez. With Bill kidnapped, the children, marooned far from the mainland, find themselves playing a dangerous game of hide-and-seek with an unknown enemy.

The holiday this time is to be in the Black Mountains. Allison is going to paint and stay at a chalet, Bill will be working, but visiting, and Hans will take the children on a pony trek for a couple of days. With the mystery of a rumbling mountain, roaming wolves, and a mad genius who plans to rule the world, the trip does not turn out as peaceful as expected.

In The Circus of Adventure the kids are looking forward to a summer break now school is over and are soon off on holiday with Bill and Allie. But Sir George has asked Bill to protect the future Prince of Tauri-Hessia who subsequently joins the kids on holiday. Soon the family is thrown in to a daring adventure as they are pursued by the baddies who plan to overthrow the King and place a puppet Prince Tauri-Hessia on the throne.

The family are on a river boating holiday in Turkey when Bill gets a call from Sir George. Will another holiday be ruined? Bill is instructed to gather information on a small time criminal who is linked to a larger gang and a stolen quantity of a deadly chemical.