There were four children who had escaped from London during the air raids. Their names were Peter, Susan, Edmund and Lucy and they temporarily moved to a Professor's house in the heart of the country, and after seeing the wildlife there, they decided to go out, but the next morning it heavily rained, so Peter suggested that they should explore the house.
As everyone seemed to agree on this idea next morning, they started looking into spare bedrooms and balconies and marvelled at the items they saw. They also passed through a dull room with only a wardrobe with a looking-glass.
Lucy, unlike the others, decided to just have a look inside the wardrobe and accidentally ended up outside. The place looked strange as it seemed to be winter in that place.
As she met Mr Tumnus the Faun, Lucy understood that she had entered a magical land which was in the hands of a cruel witch. She also was told that the real creator and leader, Aslan, was due to come at that time. All this time, Lucy did not know that this fox was a slave of the witch herself and was trying to trap Lucy and take her into the wrong hands. When Lucy found out about this, she forgave the Faun and went back.
As Lucy entered the world it seemed that time hadn't passed at all! Her siblings did not believe her, so they complained to the Professor, who was a kind-hearted man. Later, the children finally believed when Edmund saw Narnia but unfortunately joined the Witch's side when he met her in a chariot. Of course, the witch's intention was to betray Edmund and his friends as a prophecy said that the four siblings would rule over this strange land.
Aslan had finally arrived in Narnia and it was spring, the spell of the witch broke and angered her. She gathered a huge army only to realise the Narnians were already there! They had seized Edmund and the four children were also leading in the army. Narnia won, and the siblings ruled over the land for 20 years until they went back home.