Tam's a first-contact expert, and an extraordinary telepath, but also something of a maverick, annoying people by telling them their thoughts. As he prepares to give his briefing, Riker tells Geordi about Garushta (though Tam was not directly responsible, Riker thinks he should have done more to prevent it.) Later, at the briefing, Tam tells them of a recent discovery around the dying star Beta Stromgren. The Federation has discovered "Tin Man", which they think is some form of living spaceship, and Tam has to go talk to it. However, there's a hitch: the Romulans claim that space as their own, and are also sending ships (2 Warbirds) to claim Tin Man for themselves. Picard assigns Data to work with Tam on this crisis.
A few hours later, the sensors detect something odd, but it's a clear sign that they are being followed. Meanwhile, Troi talks to Tam (who enjoys Data, since he is the one being on board he cannot read), and discovers he's already in contact with Tin Man, still light-years away. As the Enterprise approaches Tin Man, a Warbird (which only ran this fast by irreparably damaging its engines) decloaks and lightly damages the Enterprise- just enough to get to Tin Man first.
Shortly afterward, the Romulans decide that if they can't communicate with Tin Man (and they've failed), they will destroy it. Tam, seeing no other option, warns Tin Man telepathically, and Tin Man destroys the Warbird instinctively, almost taking the Enterprise as well.
Later, Tam tells Picard all he knows about Tin Man: it calls itself G'amtu, is very old, and has come here to die. He claims that to obtain any more, he must go aboard it, but Picard initially refuses. Before long, the other Warbird is approaching, and when Data suggests that he beam over with Tam to keep an eye on him, Picard agrees- particularly when the other Warbird arrives and claims right of vengeance on Tin Man.
Tam is initially overloaded by Tin Man upon arrival, but quickly recovers, and ends up feeling better than he ever has. As the Romulan commander repeats his warning to stay away to the Enterprise, Tam tells Data he must stay: "this," he says, "is where I belong." As the star starts to collapse, Tin Man whirls, and sends both ships light-years away, in opposite directions. Data is returned to the bridge, awestruck by what he has seen, and later talks to Troi about Tam's healing, and says that the Enterprise is where he belongs.