Both the film and the play tell the story of a mute woman working as a janitor in a secret government laboratory who falls in love with an intelligent, aquatic creature trapped there for research. When she discovers the government's plan to kill the creature, she plots to free it.
As discussed recently on the Malloy & Malloy blog, copyright infringement requires more than the mere fact of substantial similarity between the copyrighted work and the accused work; the accused work must appropriate the original, protectable expression within the copyrighted work. By way of example, a spy thriller including a scene where the hero is introduced to her "spy gadgets" may not necessarily infringe Ian Fleming's copyright in his James Bond series, even if it is reminscent of Bond and Q. If Zindel can point to enough concrete similarities that are original to the play, however, he may be successful in the lawsuit.