Hoshi is in her quarters one night when she hears whispering and spies a mysterious figure lurking in the shadows. She alerts Reed, but when she turns back to the figure, it has disappeared. Reed scans for intruders, but nothing turns up. Later, as Hoshi attempts to translate some of the Xindi database, she once again hears voices and sees the mysterious figure. She also has a vision of being in a strange alien sanctuary. Alarmed, Hoshi visits Phlox, who examines her but doesn't find anything out of the ordinary. As they talk, the mysterious alien presence once again visits Hoshi — in the form of Phlox. He tells her that he's been studying her mind for several days and that he has a form of telepathy that only works in rare instances. He also tells her that he knows Enterprise is on an urgent mission and would like to talk to her about it.

Meanwhile, T'Pol has been studying the locations where Enterprise has encountered spatial anomalies, as well as the sensor logs from the Xindi ship. Her analysis implies that there is another sphere just like the one Enterprise encountered previously. Both spheres emit gravimetric waves — the anomalies occur where the waves intersect. Archer realizes that Enterprise may be able to use this information to predict where they will run into the anomalies. In order to do this, they need precise measurements of the second sphere's gravimetric fields, so Archer sets a course for its location.

Later, Hoshi confers with Archer about her encounters with the alien presence. She tells him that the alien is willing to use his abilities to help the crew find the Xindi. She believes he's sincere, but Archer is skeptical. Still, the captain agrees to take a slight detour and visit this mysterious alien's homeworld. Once Enterprise arrives, Archer, Hoshi and Reed head down to the surface. They are a bit unnerved when they see that the alien, Tarquin, appears to be the only inhabitant of the planet. Tarquin believes he can aid in finding the Xindi and the weapon they're building, but he will need an object associated with them. He also has one condition: he wants Hoshi to stay with him while he's working. Archer is reluctant, but Hoshi agrees to the terms.

Archer brings back the piece of debris from the Xindi probe for Tarquin to study. Tarquin uses this — along with a small, sphere-shaped object that allows him to extend the range of his telepathy — to gather information on the Xindi. As he works on this for the next few days, he attempts to endear himself to Hoshi. He serves her favorite foods, gives her a book written in a dead alien language and even shows her how to use the telepathic amplifier. He also notes that he has learned much about Hoshi from studying her memories, and believes they have much in common. Mostly, they are both familiar with solitude. Tarquin reveals that he is one of the few telepaths among his people, and was therefore sent to live out his life in exile. Hoshi is touched, but can't help but feel uneasy about Tarquin's intense focus on her

Meanwhile, Enterprise has reached the location of the second sphere and is being hit by a wave of anomalies. These anomalies are much stronger than the ones Enterprise encountered before and threaten to tear the ship apart. Archer tells Trip to insulate a shuttlepod with trellium-D and the two men take it in closer to the sphere. The shuttlepod experiences quite a jolt as it passes through the cloaking barrier, however, and the sensor relays are damaged, forcing Archer and Trip to land on the sphere to make repairs. They encounter more difficulties when Trip accidentally triggers the propulsion system, causing the shuttlepod to lift off by itself. The two men manage to shoot it down and get all the scans they originally came for.

Back at Tarquin's sanctuary, Hoshi wanders the grounds, exploring. She is surprised to discover a small group of graves. Upon finding her outside, Tarquin angrily confronts her, but she demands to know who is buried on his grounds. Tarquin reveals that these were his former companions. He sought them out just as he sought out Hoshi, and they lived in solitude with him, one after the other. Tarquin, however, has a very long lifespan, and is destined to outlive anyone he might bring into his realm. Hoshi says she is grateful for his help, but she has no desire to become his next companion. Tarquin persists, saying that no one can understand her the way he can, but Hoshi remains unmoved.

Later, Archer arrives on the planet to collect Hoshi. Hoshi is eager to return to Enterprise, and happily greets Archer when he arrives. The captain says that Tarquin was able to give them a lot of information on the Xindi weapon, and has offered to keep supplying them with data. There is, however, one condition — Hoshi must stay with him while he continues his work. Archer asks Hoshi to consider his request. She's about to relent, but suddenly realizes that Archer is actually Tarquin appearing to her as the captain. Hoshi confronts him, but Tarquin gives her an ultimatum — stay, or he will use his telepathic powers to destroy Enterprise. Hoshi responds by making her own threat. Seizing his telepathic amplifier, she threatens to destroy it if he doesn't allow her to return to Enterprise. Tarquin realizes that without the amplifier, he won't ever be able to find another companion once he out-lives Hoshi. Defeated, he allows her to go.

Back on Enterprise, Archer and T'Pol are analyzing the data collected from the second sphere. They are surprised to learn that the locations of the anomalies don't necessarily correspond with the two spheres. Thus, there must be more than two. In fact, T'Pol deduces that there must be at least fifty. Perplexed, Archer wonders if whoever built these spheres did so to create the Expanse.

As for Hoshi, she is contacted one last time by Tarquin. He promises that it is the last time and gives her the information he collected regarding the Xindi — a set of coordinates for a Xindi colony, where the species is building part of the weapon.