In the aftermath of the visit of the mysterious probe to Earth in 2286, Starfleet is wondering what this strange visitor really was about, and who sent it. At the same time, a major political upheaval on Romulus has deposed a ruling party that has ruled for decades, and the new leadership is interested in more diplomatic relations with the Federation. With the probe headed towards Romulan space, it is a chance for the two powers to work together to understand who sent the probe, and why.
Eventually, the crew of the USS Enterprise, working with Romulan counterparts, tracks down the probe, and learns more about its background and history. Spock successfully mind melds with the probe, learning that it did not seek to be destructive to other races, instead they were so different from its creators that they were ignored as "mites" in "metal bubbles", and teaches the probe to be more aware of what it is doing to humanoid life in the galaxy as it travels, leaving the probe to continue to explore the galaxy and the detente seeking Romulans with some of the first peaceful interaction they have ever had with the Federation.