Trixie, Derpy Hooves, and Lyra Heartstrings find themselves in a world called the Terminal, surrounded by gateways to other destinations. And, to their dismay, the gateway to Equestria is locked and the keys are scattered.
They need to find the keys to unlock the gateway and get home before somepony realizes they are missing.
And that means tracking down a certain DJ who seems to know why they are there in the first place.