Shere Khan, the tiger, has decided to change his hunting grounds because he has made the people of the village by the Waingunga River, twenty miles away, very angry by killing their cattle. Because Shere Khan is lame, he can't successfully hunt wild animals. Therefore, he moves near to where the wolves live because there is a human village with livestock close by. Since these human villagers don't know about him yet, he will be able to get some of their animals before they go after him.
The wolves are not happy about this turn of events. As Mother Wolf explains, the villagers will get very angry when Shere Khan begins killing their cattle and will burn down the grasses to try to flush him out. This will force the wolves and their children to have to run to escape the fire.