This is a coming-of-age storyabout two young boys, Ellis (played by Tye Sheridan) and Neckbone (played by Jacob Lofland) who both live in poverty on riverboats in the river delta area of Arkansas. With nothing better to do, they go on an adventure. They sneak off to a supposedly deserted river island where Neckbone has seen a boat snuck high up in a tree, cast there by high river waters during a flood. Neckbone wants to get the boat down from the tree, to repair it, and make it his own. He takes Ellis to help him figure out how to get that boat down from the tree.
To their surprise, the island is not deserted. A fugitive named Mud (played by Matthew McConaughey) has taken up residence in the boat stuck up in the tree. When the boys discover that Mud has also laid claim to the boat, they make a deal with him to bring him food, and spare parts to repair the boat, if he will let them keep it. Mud needs the food so he agrees. The boys come back daily with food supplies which Mud eats voraciously, having been laying low in the woods, with not enough to eat, for a long time.
The boys learn that Mud is trying to find his old girlfriend, a woman named Juniper (played by Reese Witherspoon). He is risking everything, including going to jail for killing a man just so he can see her once again. The boys accept that Mud had to kill the man because he tells them the story of why he did it. The man pushed Juniper down the stairs killing her baby because she was pregnant at the time. Mud wanted to protect the woman he loves more than anything. Mud plans to re-unite with Juniper and both of them run away together. Mud convinces Neckbone this will work because of the true love that Mud shares with Juniper.
The boys help Mud get the boat out of the tree, then steal lots of spare parts and work hard with Mud until the boat is repaired and ready to be put back into the water. The boys recognize Juniper in town from the description of her given by Mud. They contact her pretending to be selling fish, only to discover she is being physically abused by another man. They try to convince her to go to Mud but she has no further interest in being with Mud at all and refuses to go.
This confuses Neckbone because he believed it, when Mud told him that true love would triumph and not only is Juniper unwilling to run away with Mud she doesn't even want to see him again. Neckbone also has a crush on a local girl and this girl tells him to go away and leave her alone because he is too young to be her boyfriend which breaks his heart. This enrages Neckbone because he was doing all this stuff for Mud because he believed that love was real but now he is convinced that love is not real, especially because his parents are getting divorced as well.
Neckbone and Ellis go back to the island because Neckbone wants to confront Mud with all the lies about love that Mud told him. Mud trades his empty gun with Neckbone for the boat. Having no further dream for using the boat, and liking the gun, Neckbone agrees. Neckbone gets bit by a poisonous snake. Mud carries him to the hospital, risking arrest to save him. Meanwhile, the father of the man Mud killed, finds out where Mud is. He sends his other son to kill Mud. There is a big shootout and nobody is really sure if Mud is dead or alive or if he was able to make his escape down the river in the repaired boat.
Best part of story, including ending:
The setting on the river, with the worn-out boats, and the poverty which is made worse because they are losing the worn-out houseboats due to a law that passed making them all illegal. The human inter-personal drama, with this setting as a backdrop, is very interesting.
Best scene in story:
When the boys find Mud living on the island, using the boat stuck up in the tree as his temporary shelter, and they argue over who had the prior claim on the boat. The boys show a newly developing strength of character which Mud respects.
Opinion about the main character:
Even though Mud seems dangerous and definitely should not be trusted by the young boys, still he seems to be doing the right things even though the results are not legally correct.