Merwen goes to Valedon, to recruit a young Valan, Spinel, to return to Shora and attempt to learn their ways.

Berenice, daughter of the first traders to settle on Shora, spent her childhood among the Sharers and returned to Valedon to spend time with her fiancé, Realgar, a Sardish Valan general.

To Spinel's initial distress, after some time on Shora, his skin takes on a purple hue as his body becomes acclimated to the breathmicrobes that allow Sharers to stay longer underwater.

He gradually learns the Sharer way, as a man and is finally accepted by Merwen's daughter, Lystra, who risks her life to save him from a Shockwraith, a deadly underwater creature.

Lystra's former 'lovesharer', Rilwen, is "stonesick", meaning that she has developed an addictive fascination with the stones and gems the Valan traders bring to Shora.

The Sharers peacefully continue their way of life, despite the increasing military presence and escalating violence of Realgar's soldiers.

Merwen attempts to "share" with Realgar to cure him of what the Sharers consider the Valan's sickness, the fear that causes them to "hasten death" (kill).

Slonczewski's premise associates the exploitative and patriarchal practices of Valedon as males and ecological wisdom as female.

Eric C. Otto argues that Slonczewski subverts this essentialism by depicting women, not as more in tune with ecology than men, but as allies with the non-human natural due to their shared subordinate status under patriarchy and their subjection to capitalist practices.

[1] The Sharers take egalitarianism for granted because they share and they lack the concept of "power-over", making their society one in which conflicts are settled without violence.

The author based the events of their novel on much historical research, particularly the writings of peace historian Gene Sharp.

For example, the participation of children in nonviolent resistance draws on deep instinctual responses found in humans and related mammals.

[6] The women of Shora love and reproduce with each other, while homosexuality is illegal on Valedon and referred to as "immoral cohabitation.

[8] Jane L. Donawerth argues that A Door Into Ocean complicates the conventions of science fiction lesbian separatist utopias through the incorporation of a young male into the Sharers of Shora.

In an interview, Slonczewski explained that these rejections by saying, "This was before the collapse of the Soviet Union, and there was an absolute dogma that peace never works.

[8] The 1985 Library Journal review highly recommended this novel, saying "Slonczewski creates an all-female nonviolent culture that reaches beyond feminism to a new definition of human nature".

[12] New York artist, Ziemba, released a "sonic fragrance mist" in 2017 named "A Door Into Ocean", after Slonczewski's novel.