Ever since I watched the first series, I felt that the Romulans were the orphan stepchildren of the original Star Trek show. Appearing in just two episodes, evidently they were shunted aside in favor of the Klingons for the simple reason that the makeup for the latter was cheaper. Nevertheless, their first appearance (the superb "Balance of Terror") hinted at a long involvement with the Federation that went unexplored, which made them a promising source of material for authors when the original novels started rolling out in earnest in the 1980s.
Though M. S. Murdoch's novel wasn't the first in the Pocket Books series to include Romulans (a few were included in Sonni Cooper's Black Fire, published six months previously), they were the first in which the Romulans served as the main antagonists. When the novel begins theirs is an empire in crisis, ravaged by a plague that is decimating the population. Faced with their destruction, the Romulans embark on an audacious plan designed to obtain the cure from he nearest available source — a planet on the Federation side of the Neutral Zone.
As the first book to utilize the Romulans as the main antagonists, Murdoch has a good deal of latitude, and it testifies to her restraint that she doesn't overdo it. Her Romulans are true to their depiction in the original series, and point to the rich possibilities that would be developed by subsequent authors and in subsequent series. Yet this is offset by her incorporation of a subplot in which the Enterprise's computer falling in love with Jim Kirk, creating chaos aboard the ship as a result. While such a contrivance is necessary for the plot, the silliness of the concept Murdoch uses (which originated in a story she wrote for a fanzine in the previous decade) detracts from the gravity of the situation facing both the Romulans and the Federation, and might have been better saved for a novel lighter in tone.