Pumbaa builds a house for Little Jimmy, but Little Jimmy is actually a criminal, and his house is actually a hide out.
"Nest Best Thing" begins by introducing Timon, a meerkat, and his warthog friend, Pumbaa. At the start of the episode, Timon climbs a tree to catch a beetle. After he succeeds, the tree branch breaks, causing him to fall and Pumbaa getting hit in the head by the branch.
Timon and Pumbaa then meet a bluebird named Little Jimmy, who states that he lost his home. Pumbaa decides to build a new house for Little Jimmy, but Timon refuses to do so since it's too much work. When Pumbaa leaves Timon with Little Jimmy to get some tools to build a birdhouse, the bluebird suddenly changes from cute to criminal mastermind, revealing that he is a crook.
Little Jimmy forces Timon to help build the birdhouse as well as keeping his criminal mastermind nature a secret from Pumbaa, otherwise he will kill him. When Pumbaa returns, Timon is about to explain to Pumbaa what just happened until he is interrupted by Little Jimmy.
While Pumbaa reads the manuel, Timon swiftly builds the birdhouse, with Pumbaa happy about their teamwork being successful. Little Jimmy, however, is unsatisfied with the house, stating that he would like it to be bigger with different kinds of items inside. When Timon and Pumbaa finish rebuilding the house, Little Jimmy asks for a security system, an electric fence, and a mote.
After Timon and Pumbaa add the things Little Jimmy asked for, Timon tries to convince Pumbaa that Little Jimmy is dangerous, but the warthog doesn't believe him as he thinks the bluebird is too cute. But then, a group of pigeon police arrive and try to arrest Little Jimmy, making Pumbaa realize that Timon was right.
Pumbaa helps out by opening a secret entrance he and Timon built to surprise Little Jimmy. When Pumbaa gets on the roof, he uses his gas to distract Little Jimmy with the smell and then tries to get the police to catch the bluebird, but they are also distracted by the smell, leaving it up to the warthog to capture Little Jimmy, who asks him to let him go by using his fake cute nature. Knowing that Little Jimmy is a crook, Pumbaa refuses and he and Timon turn the bluebird in.
After the police thanks Timon and Pumbaa for helping them catch and arrest Little Jimmy, Pumbaa apologizes to Timon for not wanting to believe him in the first place. Timon accepts his friend's apology and states that from this day forward, they will never use any tool. However, when the police announces that Little Jimmy has escaped, Timon builds a hideout for himself and Pumbaa to hide from Little Jimmy.