One is the Lonliest Number is the second episode of the first season in Prehistoric Island.
As a new day dawns, many herbivores start to graze on plants. But as they graze, Mark hunts for some prey, especially since the baby Diplodocus from the last episode did not satisfy his hunger, so he decides to hunt for larger prey. As he hunts, he finds a Gryposaurus, and stalks it until a strange smell fills his nose. He decides to follow the smell and abandon his target.
Mark eventually finds a dead Stegosaurus. He goes near the corpse, and finds out that it has been freshly killed. He eats the corpse, but unfortunately, he let his guard down, and he senses the presence of two Allosauruses. One of them attacks Mark immediately, but he manages to shake it off. The fight immediately stops when the parents of the Allosauruses arrive. Being outnumbered, Mark has no choice but to run away.
Meanwhile at a small lake, the herbivores hanging out there become uneasy as Malachite drinks from the lake. And yards away from the lake, Mark takes a rest. The narrator talks about how life for these two has been very hard. Malachite's family has been killed of by a Giganotosaurus, while Mark is the last of his kind existing on the island.
In the late afternoon, a herd of Stegosauruses are grazing. The herd spreads out so that they can find more grass to graze on. As they graze, they make way for a family of Wooly Mammoths, who are also in the field to graze. Yards away, Mark wakes up from his nap, roaming around the plains for food. His belly has been rumbling ever since the Allosauruses chased him away from the Stegosaurus carcass. However, he becomes lucky as he sees an Olorotitan nearby. He eventually kills it off, and his hunger is satisfied.
Under the tree, Malachite, who has just had his dinner, takes a nap. Upon waking up, he detects the scent of something familiar. He follows the scent, and ends up at his family's old territory. However, he gets chased by the Giganotosaurus that slaughtered his family. Eventually, he reaches a clearing and hides in the bushes. Unfortunately, the Giganotosaurus catches the poor young Tyrannosaurus and almost kills him. Luckily, a passerby Ankylosaurus whips the Giganotosaurus using it's club, knocking it over, and releasing it's grip on Malachite. Malachite then runs into the forest.