Carol Dawson, Miami Herald reporter, is the main character. Forceful and independent, she conceals her sexual relationship with Dr. Dale Michaels of the Miami Oceanographic Institute. She frequently reacts to sexist attitudes or comments of Nick Williams, owner of the boat she charters in order to scan the sea floor for a missing Navy missile. She relates more warmly to Troy Jefferson, a young black electronics whiz and computer programmer. Eventually, she allows herself more open exchanges with Nick Williams, but she always harbors a fear of becoming emotionally close to a man — a fear she traces to her parents' divorce and her father's departure when she was very young. The memory of that loss limits her willingness to commit herself to another person in a mature relationship.
Nick Williams has the boat and the diving skills necessary for helping Carol Dawson, but Williams frequently objects to Dawson's control of their relationships, both in the business aspects and the personal aspects. The scanning equipment Carol Dawson has borrowed for the search is unfamiliar to both of them, yet they quibble over its installation and use. Hurt by a past love affair with a wealthy wife of a fur dealer (who was usually gone for long periods), Nick Williams is defensive, even chauvinistic towards women. Ten years before, Monique had led him into exotic ecstasies until he realized he was simply a current toy whom another socialite offered to pick up when Monique's husband returned to the Florida estate.
It is Nick Williams who compromises some of the results of Dawson's undersea search because he has drunk too much and embroils himself in a brief tussle with a pair of naval intelligence officers at a night club. Yet, it is Nick Williams, too, who has the foresight to return to the alien ship the gold trident that cradles the seeds for improved species of earth creatures — including an improved strain of humans. He argues that the human race as it is should be allowed to continue to learn from its challenges and grow to its potential rather than to be put into a secondary status by an improved super race.
Troy Jefferson is the bright, self-educated electronics and programming genius nearly crushed by the early violent death of his older brother. He interacts well with Nick Williams and Carol Dawson personally, and his knowledge of electronics and diving are important to the development of the plot. He is the one kept longest in the submerged space ship by the aliens and is the one told what information and materials the aliens need. Thus, he plays a vital role in advancing the plot. The video game he is programming, besides being X-rated, is ethnically sensitive, giving different responses to a player depending on the player's race. Jefferson is the target of racist comments by Ramirez, one of the Navy lieutenants investigating Carol Dawson's activity. However, since he and his girlfriend are the only significant blacks in a story involving mostly white characters, Jefferson serves only to "raise the consciousness" of a reader. He does not seriously struggle with racism as an obstacle himself, nor does his race cause any significant change in the attitudes or actions of the other characters.
Troy Jefferson's girlfriend Angie Leatherwood is a successful pop singer. Her career has taken off, so she has fame and money that Troy himself has not yet achieved, although his video game has potential. The pair are in love but are separated by career interests, so the relationship is subdued.
Captain Homer Ashford and his bodybuilder assistant, Greta, serve as modest villains for the story. Formerly partners with Nick Williams and others in a venture that discovered a sunken treasure ship, Ashford and Greta managed to steal and hide a major portion of the gold. They suspect Carol Dawson may have found another trove and interfere with her efforts both subtly and violently. Williams and Jefferson, however, find the gold Ashford has hidden and spirit away enough of it to meet the needs of the aliens. The evils which Ashford and Greta embody, thus, are sufficient to provide some conflict in the plot but are not significant enough to draw important retribution.
Other antagonists to Carol Dawson, Nick Williams, and Troy Jefferson are Navy Commander Vernon Winters and his bumbling lieutenants, Todd and Ramirez. While Winters is in charge of the investigation of the loss of the Panther missile, his character serves more to explore struggles with a conservative and pietistic view of God. Winters is one of the pilots who bombed Muammar Qaddafi's compound in Libya in the 1980s, and he carries a crippling guilt over the death of Qaddafi's little daughter. He also undergoes a midlife crisis and guilt over his attraction to Tiffani Thomas, an appealing teen-ager who plays his love interest in the closing scene of a local theater production. Todd and Ramirez directly interfere with Carol Dawson's search, suspecting that she and the others are cooperating with the Russians in an effort to find the lost missile. The two young officers enact a stereotypical crudeness in their interrogations and pursuits, but ultimately learn nothing from their exposure to the aliens.
However, Commander Winters, once he sees and recognizes the scope of the alien technology, resolves his guilts and conflicts in a doxology. The marvels of the universe shown to him he takes as God speaking to him once more after a prolonged silence. In Winters's characterization, Clarke allows scientific discovery and even contact with aliens to be interpretable from a literalistic religious perspective.