Katie Morag tries to help her busy parents by delivering the mail to everyone on the island. In a moment's distraction, her plans go awry and in trying to make things better, she actually makes things worse! But with the help of her beloved Grannie Island, she eventually sorts everything out, and learns something too.

Katie Morag has two grannies - Grannie Island and Granma Mainland. The two grannies are as different as different can be. It's the day of the Isle of Struay Show with its main attraction, the Grand Struay Sheep Contest, and Grannie Island is trying to win the prize with her beloved sheep Alecina for the eighth year in a row. Neilly Beag, however, has high hopes that his own lovely ewe will take the cup.

Struay Primary School is so small that it only has one teacher in one big mixed-aged classroom. Katie Morag's teacher announces her retirement and her plans to leave the island. Katie Morag doesn't like change at the best of times but this news, coming on top of her mum and dad having another baby, is all a bit much!

Grannie Island tells Katie the story of the Big Smelly Goat, a tale of a woman who has a lot of children and a very messy house. With the help of a wise old woman she sorts out the chaos in rather an unusual way.

The new teacher arrives at Struay Primary School, bringing with him his son John, who Katie Morag rather takes against to begin with, although she is secretly impressed by his many stories of the marvellous place he used to live in. So much so that Katie Morag begins to see Struay in quite a different light.

It is Halloween and Katie Morag has dressed up as a pirate to go around the neighbours' houses to do a wee turn and collect a few treats. But it's a stormy night and she becomes unwell, seeking refuge at Grannie Island's house.

Katie Morag is looking forward to playing a game of pooh sticks with her mum. It's her favourite game. But Mrs McColl is too busy to play, so Katie Morag stomps off to Grannie Island's house and gets soaking wet on the way. Grannie Island gives her some spare wellies that she happens to have, which once belonged to a girl called Izzy. Katie Morag is curious because she doesn't know an Izzy, so she and Grannie Island travel all over the island to see if they can find her.

Katie Morag hears the story of Stone Soup. There is something wrong with the potato crop and everyone is hungry. A young man sets out from his village to try and find work and food, and he succeeds in rather an unusual way!

Mr and Mrs McColl are going on the ferry to the mainland to await the delivery of the new baby. They leave Katie Morag and her brother Liam in the care of Grannie Island, and Katie Morag is left in charge of the family cat, Fabbydoo. But Fabbydoo mysteriously disappears...

When Mr and Mrs McColl come home with Katie Morag's new sister, Flora, everyone is so interested in the new baby that Katie Morag feels ignored. She storms out of the house feeling left out and angry with everyone. She is even angry with her dearest and oldest friend - her teddy bear.

Friday is baking day in Struay, when everyone bakes their special treats - everyone that is except Mrs McColl who, unlike Mr McColl, is not a good cook. Mr Mackie the new teacher and his wife, who is an expert baker, are coming to tea but Katie Morag's mother has written down the wrong date so there's nothing prepared, and Mr McColl is away in Glasgow! Katie Morag tries to help her mother out of the dilemma in her inimitable way - with the help of a few others!

One night Katie Morag is a little bit worried because Grannie Island doesn't flash her torch to say goodnight like she normally does. So the next morning she and her mother go to check that all is well. They discover that far from being well, Grannie Island has hurt her back and can't get out of bed, but didn't want to trouble anyone. Katie Morag thinks that Granma Mainland will be able to help, but Grannie Island doesn't agree at all!

Katie Morag is excited because her big boy cousins have arrived on Struay for the holidays. Instead of finishing Grannie Island's chores and putting up their tent as they were told to, the cousins run off to play, with Katie Morag tagging along behind. They run amok, looking for adventure, and young Katie Morag finds that she forgets some of the countryside rules in her attempts to be part of the big boy gang.

At Grannie Island's ceilidh, Mr McColl tells a story about the day Mrs Finlayson and her family have an important visitor to lunch who she is keen to impress, but Murdo, the granpa of the family, has a wee mishap which puts a bit of a spanner in the works!

Katie Morag and her classmates have a lesson on the beach, where they are all dressed in seal costumes. Mr Mackie tells them of the legend of the singing seals and all the class try to hear them but Katie Morag can't hear anything. For the next few days she does her utmost to get those seals to sing for her. Will she ever hear them?

At Grannie Island's ceilidh, Uncle Matthew tells a story about a teenage girl called Annie Jessie who lived on Struay long ago. She works hard looking after her family. One day when sheltering from a storm she meets a merboy who has lost his comb. Annie Jessie makes him a new comb from a razor shell and soon they fall in love. With the help of the sea king, who is in charge of all the creatures of the sea, they are able to go and live happily together on the island of Fuay.

It's the day of the Five Sisters Run, the annual Struay hill race. John says he can beat Katie Morag in the children's race because 'boys are better than girls at sport'. Katie Morag and her friends Agnes and Sasha are outraged, and Agnes hatches a mischievous wee plan...

At Grannie Island's ceilidh, the Lady Author tells a story about the time some wild men from the nearby island of Bickersay came across the sea to challenge Hugh Handy, the master boat builder of Struay, for the title of best boat builder of the isles. Everyone on Struay was afraid of the noisy, argumentative Bickersay men but Hugh Handy had a clever plan to make them behave themselves!

Katie Morag loves doing big paintings. She and Liam are looking for a big piece of paper to paint on, but their parents are busy in the post office and can't help them find one. After asking Grannie Island without success Katie Morag calls at the Lady Artist's house - she is bound to know where they could get one from!

Neilly Beag used to have a wee job on Struay but he isn't needed there any more and that has made him sad. Katie Morag tries to suggest other jobs he might get to cheer him up. Inadvertently, while eating a bowl of his delicious porridge, she has another one of her brilliant ideas! And that is how Neilly Beag's Brochan Bus comes to be parked on the pier selling porridge to the tourists...

Neilly Beag asks Granma Mainland to marry him and she says yes. Everyone is excited.

Granma Mainland arrives just in time for the wedding and Grandad Island arrives with her.