Why "in" is necessary when use "there"?
Native speaker’s answer
Rebecca
As can be seen in the clip Jake and Finn are spying on the other characters who are in a room. The use of "in" before "there" is necessary to emphasize the location of the other characters. They are "in the room", while Jake and Finn are outside. Ex: Is anyone in there? Ex: Maybe I should go in there and talk to him.