After 16 years, medical student Karla returns to her parents' home on Mallorca. Just like her father Hans, she has never been able to get over her mother's death.
Now father and daughter can hardly exchange a word without an argument flaring up. Karla's relationship to her stepmother Susana is also tense. Maria, her half-sister, is the only one to welcome her with open arms.
But all the family quarrels quickly recede into the background when Hans collapses without warning. After being stung by an insect, he suddenly finds he can't breathe. Karla performs an emergency tracheotomy and manages to save his life, but when he is rushed to hospital his condition begins to deteriorate rapidly. The senior physician Dr. Salazar tries everything he can think of, but there is no improvement.
When Karla notices that the skin around the sting has taken on an unusual colour, she starts her own research – and traces the source of the sting: a bee with extremely curious markings.
Not even the Director of the Entomological Institute, Dr. Alvarez, has ever seen anything like it. But can this bee really have caused her father's condition?
Karla tracks down former entomologist Ben, who now works as a taxi driver. At first he is also unwilling to believe that there could be a dangerous species of insect on the island.
But when a beekeeper recognizes this bee, Ben decides to help Karla. The two of them drive to an orange grove to collect a few specimens. They hope they can use the insects' poison to create a serum which will rescue Hans; his life is by now hanging by a slender thread.
But the bee-hive is only occupied by drones, which have no sting or poison. Ben and Karla have no opportunity to develop a serum - and it has now become clear that these curious bees are about to reproduce at such speed, it will only be a question of time before they overrun the entire island.
As they conduct frantic research into the problem, Ben and Karla find out that Dr. Alvarez himself has bred this species of aggressive and extremely poisonous bees.
When they break into the Entomological Institute in search of an antidote, Ben and Karla are arrested by Inspector Barocha, who is trying to destroy the nests with insecticides.
This turns out to be a fatal mistake. The insects are intelligent and organised enough to annihilate anybody who stands in their way. When one of the hives on the beach is sprayed with insecticides, the killer bees attack the bathers without mercy, and Maria is among the victims…