Dr. Jennifer Allen sought to find a cure for a disease known as the Gillen virus. In her search for a cure she captured infected mosquitoes and give them small doses of radiation(Now believed to be the same form of Radiation that created the Doomtrooper). The levels of the radiation have to be exact because if the mosquitoes receive too much radiation, the results could be more devastating than the virus itself.
When moving to human trials the condemned criminal Ray Erikson joins Dr. Allen's program in exchange for a lifelong prison sentence. However he manages to escape and take a hostage to convince Dr. Allen to open the door to the experiment room, during this time security guards open fire on Ray and cause an explosion that showers both Ray and Dr. Allen with chemicals and the genetically altered mosquitoes. Ray manages to flee the scene heading towards his girlfriends house, unknowingly changed by the explosion.
An unpredictable mutation caused Ray to mutate drastically into a human-mosquito hybrid with an insatiable thirst for blood. After his transformation the Mosquito human hybrid feeds on his girlfriend, killing her.
Dr. Allen returns home to her boyfriend, Baltimore Police Lieutenant Tom Randal. That night she discovers raw looking flesh on her wrist that spreads to her entire arm by next morning. Dr. Allen begins to exhibit a sudden craving for blood after she bites Tom during a kiss, which causes her to rush into the bathroom where she discovers her arm bleeding before she begins to violently convulse and falls to the floor.
Tom later arrives home of Rays girlfriend and discovers her dead and drained of blood. After being called to investigate another crime scene, he encounters Mansquito. Tom fights the monster and nearly dies as a result until Tom shocks it with a stun gun, making the Mansquito flee in pain.
Dr. Allen returns to her lab where she discovers she is changing into a human-mosquito hybrid, but at a greatly reduced pace due to receiving a much smaller dosage than Ray. After this discovery she encounters the Mansquito who merely observes her for a moment before leaving. Dr. Allen faints and is discovered by Tom who brings her to the Hospital.
Dr. Allen becomes convinced that the Mansquito senses that she is soon to become something like him, and is waiting for the transformation to complete before he attempt to mate with the resulting creature Dr. Allen will become.
During this time the Mansquito mutates further by spontaneously growing fully functional wings.
After several fights with the Mansquito, all of which fail, he manages to make it to the lab after Dr. Allen who mutated further, managed to releases the last batch of genetically altered mosquitoes, which have been perfected.
Dr. Allen attempts suicide but is stopped as the Mansquito arrives, Tom manages to fight against the creature, managing to injure it again when he uses his taser. Seeing this, Dr. Allen breaks an electrical line and electrocutes both herself and Mansquito to death.
While eventually the Gillen virus indeed was wiped out by the altered mosquitoes. It is unknown if all the released Mosquitoes were perfected.