The crew of the Enterprise must bring back whales to their future in order to save Earth.
A stable wormhole is discovered and it will change the Alpha Quadrant forever in the DS9 pilot episode
A Klingon madman has stolen the plans for the Genesis Device and is headed to the planet to learn its secrets.
Khan escapes his imprisonment and threatens universal Armageddon.
A vessel of unknown type and origin hidden in a cloud is heading straight for earth and apparently destroying everything in its path. The Enterprise must intercept the vessel and stop it before it ever reaches earth.