Donnie gets lost in the Rain Forest. As Eliza searches she realizes he may be heading home to look for any of his remaining family.

The Thornberrys are in Tanzania, Africa to film the Grand Opening of Dr. Jane Goodall's Chimpanzee Sanctuary. Eliza can't wait to meet her idol Dr. Goodall. When they arrive Debbie is put to work caring for baby chimps in the nursery while Eliza and Dr. Goodall have an awkward first meeting. She is not impressed with Darwin and the fact that he is domesticated. Eliza's feelings are hurt and she runs off into the jungle with Darwin following. Trouble ensues when they run into poachers who have been working nearby.

Donnie searches the jungles of Borneo for his ancestry, causing Eliza to worry that he will break ties with the Thornberry clan.

A fire breaks out in the forest and Donnie is blamed; can Eliza convince it wasn't Donnie and get the animals to safety? Meanwhile, Marianne and Nigel find shelter in a cave nearby, only to get lost inside, and Debbie and Sophie help the village put out the fire, while learning about Donnie's real parents.

The rest of the fire is put out by the rain. The others are reunited and Donnie is found. The family believe he is going back to his parents, but they soon realize the truth.

Eliza tries to talk Darwin into taking a hot air balloon ride, knowing full well that he's afraid of heights. After being pushed around one too many times, Darwin stands up to Eliza and refuses to go.