Strange lights on the nearby mysterious island leads to the four's first adventure inside an abandoned copper mine and a network of secret undersea tunnels.

Philip and Dinah's mother takes the four on a summer adventure to a valley in the countryside overlooked by an ominous abandoned castle.

When the plane lands they find themselves in an unfamiliar valley scarred by war and, once again, the four children fall into an adventure involving a lost treasure sought by a band of villains.

Ominous rumblings from the ground, a pack of wolves roaming the area, a black fugitive, and Philip's disappearance are but a few of the mysteries the children have to unravel about the mountain.

But when Micky, Philip's new monkey, breaks his birthday present, all the children are plunged into an exciting quest to find the lost treasure of the Andra with some ruthless villains hot on their trail.

The TV series also introduced a character who was not in the books- Sir George Houghton, Cunningham's rich, underworked boss, who appeared in every episode except "The Valley of Adventure".

A running gag was that he always phoned Cunningham with an urgent assignment just as the family were planning a holiday- in "The Ship of Adventure", Bill had to postpone his wedding for this reason- yet Sir George appeared to be a gentleman of leisure.

He was only seen doing real work a couple of times in the entire series- he was shown playing pool and golf, and on one occasion, he was seen fishing, though he lied that he was in the office.

[8][9] The Island of Adventure was adapted into a 1982 British film directed by Anthony Squire, and starring Norman Bowler as Bill along with Wilfrid Brambell and Eleanor Summerfield.