On a sunny afternoon Paul and his friends, the cat Kira and the dog Hugo, meet at the playground and play a fun guessing game. "I spy with my little eye something that is ... blue!", calls Paul. Kira and Hugo look around and start guessing cheerfully: "The sky?" – "The slide?" – "The car over there?" – "The sea!!!", a voice calls from above their heads. "I've seen it often from the air." Paul and his friends look up in surprise. It's the parachuting frog, making one of his brave jumps again and landing with flair in the sandpit. Then he folds up his parachute and hops off in a hurry.

Kira and Hugo continue guessing for a while what Paul might have meant, but they just can't work out the answer. "The last coach of Uncle Egon's railway is blue!", Paul finally shouts. "Look, the engine is over there at the station!" "Oh, that really was tricky!", Kira complains. "Tell me, have you ever seen the sea? I haven't," says Hugo. Paul and Kira shake their heads. "What if we ask your uncle to take us to the sea sometime?", suggests Hugo. Paul and Kira are immediately thrilled by the idea. Paul's uncle is very kind and is happy to take them on a day trip to the sea – but first they must ask their parents for permission. They are due to set off tomorrow.

Paul can hardly sleep for excitement because he cannot wait to finally see the sea! Unfortunately, overnight Hugo has come down with a sore throat and a fever and cannot join Paul and Kira. "Have fun at the sea!", calls Paul's mum. "We'll pick you up again this evening." The locomotive toots loudly in farewell, pulls away and soon Kullerbü station is behind them.

Paul and Kira let the wind kiss their faces and enjoy the lovely journey – past brown fields and green meadows where plump cows are grazing. And then, after a while around the next bend, the beautiful, deep-blue sea appears. The seagulls cry overhead and along the long yellow sandy beach there are many parasols, sunbeds and beach chairs. "Right, we're at our destination!", calls train driver Egon as he brings the train to a halt at the nearby station. While the coaches are unloaded and reloaded with new freight, Uncle Egon is free and can go to the sea with Paul and Kira.

First he buys a huge ice cream for the two of them and then they explore the beach together. The waves form small white foam crowns and lap evenly ashore. Kira and Paul giggle with excitement the whole time. At last they find a lovely spot where they can build a sandcastle. Uncle Egon helps them with it and then makes himself comfortable in a beach chair to rest.

So the day at the beach flies by and Paul and Kira are really sad when it's time to go home. As a farewell they take a souvenir photo of the sea. And as they board the train again, Paul calls happily: "Goodbye, dear sea. We'll visit you again soon!"