has escaped his time period and is now running amok in the space-time continuum. Once inside, Doc reveals some of the inventions he had been working on, including his "crowning achievement" – an 8-passenger DeLorean time machine (also a convertible), which is what the riders will be using in the experiment. Unbeknownst to Doc, Biff has infiltrated the Institute – he appears to the riders, asking for assistance in finding Doc's time machine. Heather then announces that the pre-flight system checks were in progress and informs the riders to stand by for an announcement from Doc. Biff traps Doc in his office, and it was revealed that when one of the time traveling teams was conducting an experiment back in 1955, Biff stowed away. He takes the DeLorean and vanishes into time. Worried about the havoc Biff will cause to the space-time continuum, Doc frantically pleads with the riders to assist him and says that the only way to bring Biff back to the present is to accelerate to 88 miles per hour and bump him (which will open a time vortex that will send both time vehicles back to their original point of departure); they enter the 8-passenger time machine, led by one of Doc's assistants; after going over final safety instructions. Doc then informs the riders that the time vehicle Biff has stolen had a sub-ether time-tracking scanner; that way whatever time period he may be, the riders' vehicle will pin-point to that exact location. They then follow Biff into time. Ride When the time machine's doors close, Doc uses his remote control to control it, hover it, and accelerate to 88 miles per hour (with electric sparks coming from it, speeding through the open door and passing through the wormhole) and the ride begins. First, Biff leads the riders to Hill Valley in 2015 where they chase him through town. They smash into neon signs, fly over neighborhoods and the town square, and the chase culminates at the iconic clock tower. He then departs for the ice age. The riders follow, and slowly lower into the icy caverns. Biff honks his horn, causing an avalanche that damages the riders' vehicle. Flying out of the caverns, the riders see Biff shoot away into time, but their own engine had failed, and begins to plummet down a chasm. Doc manages to restart the vehicle, accelerating backward and through time