The crew of the newly commissioned UHS Mercy, a dedicated hospital ship, led by the enigmatic Dr M’Benga (formerly of the USS Enterprise), are thrown in the deep end when they are sent to aid the people of Cainus. The planet, peopled by two separate species—the Drackhans and the Agmorrans—is in turmoil due to an invasion by the Klingons. For many years, the Drackhans have subjugated the physically smaller Agmorrans and treated them as little more than slaves. However, the recent subjugation of the Drackhans at the hands of the Klingons has changed the perception of several of the planet’s inhabitants. The UFP, after removing the Klingon aggressors, has been tasked with negotiating an agreement between the Drackhans and Agmorrans. This effort is stymied by the resistance of a group of extremists led by Lord Kralloch. A leader among the more militant Drackhans, Kralloch is determined to foil the actions of the UFP peacekeepers and return the planet to its former “glory”. He will stop at nothing to achieve these goals, going so far as to take hostages and plot the murder of High Ambassador Sarek. Initially called to Cainus to provide humanitarian relief, the UHS Mercy is soon pulled into the planetary conflict, and members of the crew are tested in ways they could not have imagined on this their inaugural voyage.