Clive (Adrien Brody) and Elsa (Sara Polley) are biochemists/geneticists who work for a cutting edge pharmaceutical company and are also a dating couple who are trying to have a child. They have combined various animal DNA (spliced it) to create a brand new species, one male and one female (Fred and Ginger respectively). Their corporate bosses demand the two devote their resources to drawing forth a lucrative protein from Fred and Ginger which will be used for great profit in the livestock industry. Angered at their new orders, Clive and Elsa, without authorization, divert some of the resources to splice together human and animal DNA, just to see if they can, only to have the new human/animal hybrid Dren (Delphine Chaneac) be born months ahead of schedule. Dren is a female, born with a poisonous stinger and the ability to breathe underwater.
After a disastrous public unveiling of Fred and Ginger, where it is discovered that Ginger has turned into a male, the two animals kill each other, humiliating the corporation. The lab is placed under new management with William (David Hewlett) at the helm. Needing to keep Dren a secret, the scientists move her to an old secluded farmhouse. Dren continues to grow old at an inhuman pace and soon discovers she can sprout wings. As Dren becomes more intelligent and unruly, Elsa cuts off Dren's stinger (which grows back) and uses it to derive the protein for the corporation. Meanwhile, Clive discovers that Elsa spliced her own DNA to create Dren, becomes attracted to Clive, and eventually Elsa catches he and Dren having sex. They decide that they have lost control of the Dren "experiment" and decide to kill her, but Dren is seemingly dead when they arrive to end her life, and they bury her. At this point William, and Clive's brother/scientist Gavin (Brandon McGibbon) have discovered the Dren experiment and show up at the farm demanding they hand Dren over.
Alas, Dren is not really dead, but like Ginger, has turned into a violent male creature. Dren, now male, digs himself out of the grave and quickly kills William and Gavin, and knocks out Clive. He then chases, catches, and rapes Elsa. Clive having recovered, stabs Dren through the chest mid-coitus, but Dren turns around and kills Clive with his poisonous stinger. Elsa then manages to kill the injured Dren by crushing his head with a rock. At the end, Elsa is meeting the CEO the pharmaceutical company and is given a multi-million dollar check. Elsa stands up to reveal that she is pregnant, but it is unknown whether the child's father is Dren or Clive, and it is also unclear whether the check was to purchase her child or to rehire her to continue her splicing experiments.