Professor decide that their only hope of returning to the 31st century is to continue forward in time until they reach a period in which a time machine that can travel to the past has been invented. However, they are repeatedly sidetracked during their travels, encountering numerous periods of Earth civilization (at one point managing to find a time period populated by beautiful women who have mastered backwards time-travel, but are sent forward by an angered Bender, who was not let off in an era where robots were conquering humanity), until they arrive at the year One Billion when Earth is barren and all life extinct. Back in the 31st century, Leela takes over Planet Express and turns it into a successful company for over forty years, but still harbors some nostalgia and hurt toward Fry for standing her up before his "death". In the year 3050, she finds the lost birthday card as it emerges from the time stream and learns that Fry did not mean to abandon her. She goes to the empty Cavern on the Green and fires her laser at the ceiling in a way that results in mineral water dripping to form stalagmites that create a message Fry discovers one billion years later, reading that although their time together was short, it was the best time of her life. Having lost their opportunity to return home, Fry, Bender, and the Professor resign themselves to going to the end of time. After the last existing proton decays, they are amazed to discover that the now empty universe undergoes another Big Bang, and furthermore that it replicates the same universe and its exact events, as opposed to having unique inhabitants and history. They realize that they can continue forward in time and eventually reach the moment that they left in the new copy of the universe (although the Professor takes to opportunity to assassinate Adolf Hitler). They succeed after overshooting their first attempt (with the Professor accidentally killing Eleanor Roosevelt whilst attempting to assassinate Hitler a second time), though the new universe is about 10-feet lower than the previous one, causing the time machine to crush their duplicates in the new universe to death as they enter their machine (avoiding a time travel paradox). Fry rushes to meet Leela and manages to make it to their date on time. After dinner, Fry apologizes for losing his birthday