Species 2 Commander Patrick Ross leads a crewed mission to Mars. The soil samples taken by the astronauts are, in the course of their research, contaminated by an alien substance that thaws in their capsule due to the change in temperature and contaminates them, causing an unintentional contact delay of seven minutes with the mission control. The three astronauts returned to Earth to celebrate the occasion, without any apparent negative effects. Only an institutionalized former scientist Dr. Cromwell, reacts to their return in a state of panic. Meanwhile, Dr. Laura Baker has created an artificial clone Sil named Eve who’s alien DNA has been suppressed to make her more gentle. Her team is conducting experiments on Eve in hopes of finding ways to fight the alien race should it ever come back to Earth. Eve’s body adapts to each experiment, and each is unsuccessful.
Upon their return, the team members are advised to avoid sexual activities for 10 days. Patrick ignores this warning and forms a threesome including two sisters Marcy and Lucy in the wake of a fundraiser. When he has sexual contact with Lucy and Marcy, Patrick begins to grow tentacles. Lucy observes his transformation as she is touching his body. She is shocked by his appearance and tries to escape his grasp. She begs him to stop but he refuses to listen when he reaches a climax. Marcy and Lucy both suffer from hyperfertile alien seeds, which cause them to have an increased number of pregnancy. This culminates in Patrick’s alien children burst from their stomachs. His rapidly growing sons are kept under wraps by Patrick, Senator Judson Ros. Each time Patrick is sexually active, Eve experiences excitement. On the following day, Patrick tells his father he cannot recall the events of the previous night. Senator Ross declares that he’s aware of Patrick’s behavior and advises him to concentrate on his political goals.
Dr. Orinsky is one of the NASA researchers who studied Patrick. He discovers something wrong in his blood sample, and desperately attempts to contact Cromwell. Orinsky is then attacked by a substance made out of Patrick’s blood and taken to the hospital. Laura finds out that the DNA of Orinsky’s wounds differs from Eve’s, which makes her a unlikely suspect for the murder. To end the threat the Colonel Burgess the military commander of her brings Laura back together with Press Lennox. Press and Laura are able to locate Cromwell who was Orinsky’s former professor who has discovered that aliens had attacked and destroyed Mars in ancient times. In the event of his concerns that alien DNA could linger on Mars to spread disease to anyone who visits Mars in the future, Cromwell urged the government to cancel the mission however, he was adamant about an institution that would never allow him. Cromwell declares that the night Orinsky tried to contact Cromwell was to prove that he was right all along.
Press and Laura determine the Mars astronauts as the main suspects. Unable to find Patrick, they pursue two other astronauts: Anne Sampas and Dennis Gamble. They arrive late enough to prevent Anne from having a sexual relationship with her husband which results in her impregnation with hybrid offspring. Before Press and Laura can take down the monster the tentacle-like creature explodes from the abdomen of Anne. Another team of agents arrives just in time to find Dennis and check that he is healthy. Laura finds out that Anne has the genetic code of a hybrid that is not compatible with the Orinsky’s. Patrick is the murderer. Meanwhile, Patrick has sex with his partner, which results in her death as a result of the birth of another hybrid son, named Portus. Patrick is tempted to commit suicide, astonished by the fact that he is responsible for her death. But the alien DNA that is regenerating Patrick’s head and restores his life. It also temporarily eliminates his human side. Dennis is present to witness this, and he informs Press as well as Laura about what he saw. He also remembers what transpired inside the capsule and is part of their mission. Patrick starts to immunize the most women he can and hides his victims from view, possibly having up to 20 children on the father’s land. Species 2 HD
Laura is ordered to activate Eve’s alien DNA to ensure she can psychically locate Patrick, but this makes her volatile and strengthens her alien instincts. Patrick is able to surrender to Press and Dennis after attempts to rape Darlene after which he is made aware of Eve and is taken to the lab despite their suspicion. Eve begins to show signs of heat when Patrick is taken into custody. Patrick demanded Laura open Eve’s cells and was close to killing her. However, Dennis and Press drove him away with the use of a gaseous weapon. Burgess confronts Ross and presents him with an undisputed proof of Patrick’s health. He asks for his assistance in capturing Patrick. It is believed that Patrick will instead be killed, Ross deduces that he is on the property and apologizes for having treated his son so cruelly. Patrick briefly returns to his human self, but as he embraces his father, and weeps with him, the alien DNA emerges in a violent manner and kills him. Ross’s death completely destroys Patrick’s humanity. He assists his hybrid children to form a cocoon, which means they can soon begin mating and will soon be preparing for the destruction of humanity.
At the lab, Laura discovers Dennis did not have the disease because Dennis is a victim of sickle-cell disease because the species is not immune to human genetic illnesses. They are planning to utilize this weakness to gain advantage, but Eve escapes her prison to find Patrick. With Burgess as well as the military and Laura following, Dennis, Laura, and Dennis continue to pursue. At the shed, they kill Patrick’s offspring while Eve and Patrick transform into their alien bodies and begin to mate. The mating stops when Press and Dennis intervene, allowing Eve to free herself; Patrick, transformed into another alien-like form, allegedly attacks Eve by pushing his tongue into her throat. Patrick is attempting to strike the group, but Press injures the male alien with a pitchfork sprayed with Dennis’ blood. He passes away shortly afterward.
The military steals Dennis, Laura, and Press away. Eve’s lifeless body is loaded into an ambulance. But within a short time, her womb begins to grow rapidly — indicating her life and the impotence of Patrick — and Portus, who somehow survived, watches. The screen cuts to black as Eve’s uterus bursts and her screams can be heard. This leads into the third movie.