The Gladers (also known as Group A) discovered that they were not the only test group when they met Aris Jones at the beginning of The Scorch Trials. Aris told them that he had been part of Group B. It was composed almost entirely of girls, with Aris being the only boy. During their Maze Trial, they escaped from the Maze three days faster and lost fewer people than the Gladers, showing that they are fairly capable.
The leaders were Harriet and Sonya (until Teresa joined them in the Scorch). Several of the girls' roles seem to be equivalent to those of the Gladers, and the experiences of the two groups in the Maze appear to have been extremely similar. One major difference was that Rachel (Thomas's equivalent) was killed by Gally's equivalent in Group B, but with the Gladers, Chuck was forced by WICKED to jump in the way of the knife Gally threw at Thomas.
Before Group B began the Scorch Trials, they were told by Janson that they must kill Thomas if they wished to receive the cure when they arrived at the Safe Haven. They were allowed to travel through underground tunnels through the Scorch, while the Gladers were forced to travel overland in the burning sun. After they ambushed the Gladers, took Thomas, and dragged him up into the mountain pass, Thomas convinced them not to kill him. Group B and the Gladers met up at the Safe Haven, and they fought together against the Bulb Monsters before being rescued by WICKED.
In the story “True Maze”, Group B welcomes Aris to their Maze. There are eight girls in their maze and all are shocked when a boy comes up the box. Their Maze is in a snowy area and is completely frozen. They call themselves “Icers” and they call their Glade the “Spring”. Instead of Grievers, they have giant, flying, winged bat-like creatures called Shades. In the story, the Shades dwell in the outer reaches of the Maze and seem indifferent to the time of day. When the doors open in the morning, all the girls map the Maze in ice skates. They reach an ice mountain and all climb it. When Aris first tries this, a Shade attacks the group, killing Ximena and injuring Rachel.
Aris and Rachel use their time out of the Maze to map patterns that Aris discovered on a Shade’s wing. They cut open the Shade and find a transmitter. Rachel presses the button hoping for the best, but it releases Shades into the Spring. As the Icers try and fight the Shades, the transmitter turns green and WCKD soldiers arrive to save them. The only survivors were Harriet, Sonya, Aris, and Rachel. This story is only canon to the movies as in the books Group B’s Maze was the same as Group A just with different kids.