

However, before the ship can complete the rescue, it loses its last crystal, and undergoes a transposition into the mirror universe. Sulu, however, tells Chekov that they are nearly within transporter range, and Excelsior continues into the vortex. Upon impact with the storm, Chekov attempts to warn the Excelsior off, saying Enterprise-A's warp core is about to breach. While aiding the Ranger, Commander Chekov, commanding the Enterprise, has become caught in the throat of the Janus Prime Vortex, a subspace whirlpool which somehow exists in Federation and Tholian space simultaneously. On stardate 9585.9, Captain Sulu and the USS Excelsior proceeds at maximum warp, shattering most of her dilithium crystals, on an intercept course with USS Ranger and USS Enterprise-A, answering their priority-one distress call.
