They must send Jenny and Silverthorn back to their respective times, in order to restore the timeline. Silverthorn, having faked remorse for his crimes, has surreptitiously stolen instructions for building the Time Gate.
They must send Jenny and Silverthorn back to their original timelines, in order to repair the timeline. Meanwhile, Silverthorn, having pretended remorse for his misdeeds, has secretly acquired plans for constructing a time-traveling device.