A young boy, known as the Runaway Kid (Nintendo switch version, “The Kid”), wakes up from a nightmare involving him swimming in darkness before being dragged underwater. After leaving the Nursery, he spots the Janitor chasing one of the escaping children. The Kid follows a girl who is also fleeing, but she disappears and leaves her flashlight behind, which the Kid takes.
The Kid finds himself in the Depths of the Maw, which are heavily flooded and he has to avoid Leeches and make his way across by hopping on floating platforms. The Depths turn out to be the home of the Granny, who swims underwater and attempts to grab the Kid either by bumping and destroying the platforms he stands on or snatching him if he is in the water for too long. After pushing a television set into the water to electrocute and kill the Granny, the Kid makes his way to a tall wooden staircase with light coming through the top. He then reaches a ladder and climbs it, pushing through a grate. However, the light turns out to be a flashlight and he is caught by the Janitor and dragged into the darkness. The final scene shows the Kid in a cage next to other cages with children, including Six. The Janitor's long arms reach out and grab the Kid's cage and pull it off screen, paralleling Six's campaign just before she wakes up in the cage.
Source: Wikipedia, "Little Nightmares", available under the CC-BY-SA License.