Our hero Ali and his best friend Zeynep find a mysterious book on their way home from school. The cover of the book reads: "Journey to the World of Integers". They open the book with curiosity and suddenly find themselves in a strange world.

There are numbers flying around Ali and Zeynep, some in blue, some in red. A guide appears: Mr. Number. "Welcome! You are in the world of positive and negative integers!" he says.

Mr. Number shows the children a number line. "This is our map," he says. "Blues are positive numbers, reds are negatives. This line has a special power that starts from zero."

"But why do we need negative numbers?" said Ali, confused. Mr. Number smiles. "Come, let me show you!" he says and takes them to the Elevator Tower.

In the Elevator Tower, floors are expressed with positive and negative numbers. "Zero is the ground floor. The floors above are expressed as positive, the floors below as negative," Mr. Number explains.

Zeynep wonders: "Can we see where else negative numbers are used?" Mr. Number takes them to the Warmth Forest. Here the temperatures are written on the trees: +30°C to -10°C.

Mr. Number suggests a game: "List the temperatures using the whole number line!" Ali and Zeynep get the order right and solve the secret of the forest.

Their next stop is Comparison Mountain. There are two large tiles here: one +5, the other -3. "Which stone is bigger?" asks Mr. Number.