Tito and Bimbo lived under the wall where it joined the inner gate. They really didn't live there, they just slept there.
As the people of Pompeii used Mt. Vesuius as a weather guide, they noticed that the smoke from the mountain was hundreds of feet higher.
As bimbo and Tito are sleeping the air starts to taste like a powder that burns Tito's eyes and nose. As they wake up they notice strange noises from under the ground. They start to run after they realize what is about to happen.
While running, Tito trips and falls onto the ground. He falls asleep and doesn't get up. Therefore, Bimbo bites him and Tito gets up and starts running again.
Tito and Bimbo run all the way to the ocean and Tito faints midway. When he wakes up, he is on a boat with other men. He looks around for Bimbo but he is nowhere to be seen.
Tito ends up having to leave behind Bimbo but Tito lives and now has the honor to say his loyal dog saved his life.