Genetic engineers Clive Nicoli and Elsa Kast hope to achieve fame by splicing animal DNA to create hybrids for medical use at the company N.E.R.D. (Nucleic Exchange Research and Development). Their work previously yielded Fred, a dog-sized vermiform creature intended as a mate for their female specimen, Ginger. After successfully mating them, Clive and Elsa plan to create a human-animal hybrid that could revolutionize science. Their employers Joan Chorot of N.E.R.D. and William Barlow forbid them from doing this. Instead, they are to find and extract proteins used for commercial drug production from Fred and Ginger. Clive and Elsa, however, disobey their superiors and pursue their own agenda in secret, developing a viable prepubescent female creature. Although they had planned to terminate the hybrid before it reached full term, Elsa persuades Clive to let it live. They discover that she is aging at a vastly accelerated rate. Elsa discovers that the creature is undergoing mental development such as that of a young human child. Elsa names the creature "Dren" after the creature spells out NERD, having seen the letters on Elsa's shirt.

After moving Dren to a new location for fear of discovery, they find she has a dangerously high fever. In an attempt to save her they place her in a large industrial sink filled with cold water. Later on Clive fully submerges Dren in the sink, and in doing so discovers that Dren is amphibious, but it remains ambiguous whether he tried to save Dren or kill her.

While studying Dren, Elsa and Clive neglect their work with Fred and Ginger. At a highly publicized presentation of their work, Fred and Ginger savagely fight to the death. It is subsequently discovered that Ginger had spontaneously changed to a male, but Elsa and Clive failed to notice because they were focused on Dren.

Elsa forms a motherly bond with Dren. After Dren jumps on Clive's brother, Gavin, they move her to an isolated farm. There, Dren displays carnivorous tendencies and retractable wings. She grows into adolescence and becomes bored with being locked up in the barn, but Elsa and Clive fear that letting her outside might lead to her discovery. Clive realizes that the human DNA used to create Dren was Elsa's, not from an anonymous donor as Elsa had told him. After Dren exhibits dangerous misbehavior Elsa restrains Dren and removes her stinger, using it to synthesize the protein that Elsa and Clive had been searching for.

Meanwhile, Dren and Clive have developed a mutual attraction. Elsa discovers them having sex in the barn and is horrified. Clive accuses Elsa of never having wanted a "normal" child because of her fear of losing control; instead she chose to raise one as an experiment, where control could be assured. Deciding the only solution is to terminate Dren, they return to the farm and find Dren seemingly already dying.

William Barlow discovers human DNA in Dren's protein samples and arrives to investigate. Elsa tells Barlow that Dren is dead and buried behind the barn. However, Dren, having metamorphosed into a male, rises from the grave and attacks the group, killing Barlow and Gavin before raping Elsa. Clive attacks Dren to save Elsa, but Dren overpowers him. Elsa intervenes and is about to kill Dren, but she hesitates, which allows Dren to kill Clive. Elsa then kills Dren.

Elsa is later informed that Dren's body contained numerous biochemical compounds for which the company begun filing patents. Joan offers Elsa, who is traumatized by her ordeals and now visibly pregnant with Dren's baby, a large sum of money to go through with the pregnancy, which Elsa accepts.

https://en.wikipedia.org/wiki/Splice_(film)
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