Roger, Diana, Snubby and Barney just love solving mysteries – with Loony the dog and Miranda the monkey to help! The holidays will be fun, think Roger and Diana, despite having to have extra lessons. After all, their cousin Snubby is staying with them, they make a new friend called Barney 'and' there's an abandoned big house to explore nearby. But when Barney disappears the children begin to worry about the strange behaviour of their new tutor…

Barney, Roger, Diane and Snubby love solving mysteries, with the help of Loony the spaniel and Miranda the monkey. Rare and valuable papers have been stolen from collections kept in secure rooms with locked doors and barred windows. How does the thief escape without a trace, and when will be strike again? Could there be a connection with the fair travelling around the area?

When Roger, Diana, Snubby and Barney go on holiday to Ring O' Bells village, they are eager to explore the secret passage in Ring O' Bells Hall. Is it really a dead end as they have been told, or does it follow the route marked on the old map they find?

Brief Summary by Robert Houghton: On a summer holiday in the seaside town of Rubadub, Roger Diana, Snubby and Barney witness sinister goings on – explosions at the secret submarine base, suspicious characters at the old inn, lights flashing at night. Suddenly they are plunged right into the middle of another mystery and of course are determined to solve it! Barney finds work in a Pierot show to be near his friends, and begins to realize that this theatrical setting gives him an excellent opportunity to find his long lost actor father – but who is the saboteur at the submarine base, and who can be trusted? It seems that almost everyone at the inn has something to hide!

Barney, Roger, Diane and Snubby love solving mysteries, with the help of Loony the spaniel and Miranda the monkey. A cosy old house surrounded by snow-covered hills seems a perfect place to spend the winter holidays, but the peace is disturbed by unexplained noises. Who could have knocked at the door in the middle of the night, and what is the noise that Snubby hears coming from the kitchen?

Barney, Roger, Diane and Snubby love solving mysteries, with the help of Loony the spaniel and Miranda the monkey. Three weeks' holiday near beautiful Merlin's Cove in Wales sounds like great fun to the four friends, and they plan days full of swimming, ice creams and picnics on the beach. But then Snubby gets hold of a letter written in secret code, and the subsequent events make the friends realise that some sinister dealing are taking place.

Nick and Katie and their neighbours, Mike and Penny, are enjoying the end of the summer holidays. When Uncle Bob comes to stay for a rest, he seems a bit bored without his exciting private investigator's job to do, so the children invent a mystery for him to solve. But life soon becomes very exciting when cracking the children's code leads to a real-life mystery with serious consequences.