I believe I read this in the late 90s. And like the title says, a human has this team, don't recall if it is all human or if there might be an alien or two mix in. Anyways, main protagonist discovers some kind of anomaly that is spreading out from multiple alien artifacts. Most people have forgotten that things move at the speed of light since faster than light travel is quite common. But, based on how these anomalies spread out from these alien artifacts, the ripples will hit a certain spot all at the same time.
The team travels to this spot, and then they get teleported or somehow otherwise travel to an alien space station. Same species that made the artifacts. This alien species has been collecting other species for some reason I don't remember. Eventually, the main protagonist's group has to fight an extremely dangerous alien race that was supposedly, and intentionally, wiped out by everyone else. Main protagonist's team is out gunned and outnumbered, but through some great old human ingenuity, wins the day.
Then everyone leaves, and main protagonist goes to warn everyone else that some of the very dangerous aliens were also able to leave.