In "The Adventures of Huckleberry Finn" by Mark Twain, Huck and Jim begin their journey down the Mississippi River in order to avoid Jim's capture. Being an escaped slave, Jim is subject to a bounty, which places him in danger. Prior to this, Huck and Jim had been living quite comfortably on an island; however, the smoke they produced was eventually spotted by a woman onshore.
The pair intend, at the beginning of their journey, to leave the Mississippi River upon reaching the mouth of the Ohio River, which they would then navigate towards the free states in the North.
For Jim, the journey is one of necessity for his own survival, although it does mean leaving his wife and children behind.
Huck accompanies Jim out of friendship, but also because he has no reason to remain in their original town of St. Petersburg. Not only was he tired of the oppressively staid life he had with his adopted mother, Widow Douglas, and her sister, Miss Watson, but he also wished to avoid the only legal alternative, which was returning to live with his drunken, abusive father. In order to escape either fate, Huck faked his own death by slaughtering a pig and covering his father's cabin with its blood.