One morning, lying in the grass, Santiago experienced something that changed everything: a solar eclipse that had been predicted by scientists. The sky went dark in the middle of the day. And he became obsessed with a question: how could those people know the exact day and time the sun would disappear? What superpowers does human intelligence have? What is inside our brains?

At school, he stood out for his curiosity and his rebellious streak. He refused to memorize everything because he was bored to tears, driving his teacher up the wall, until he finally got himself expelled. By day, he started working as a barber; by night, he accompanied his father to the cemetery to learn anatomy, drawing skeletons. That was how he returned to school, strengthened by a newfound purpose: to become a doctor.

He finished medical school and began his new life with an adventure: heading off to a war in Cuba to save lives. That was until a mosquito attacked him with a killer parasite, and he lost that battle. He returned home skinnier than the skeletons in the cemetery.

Back in Spain, he decided to settle down. He fell in love with Silveria. Together, they had seven children and the stability he needed to research... cells! Using the family’s savings, he bought a microscope. And with just a few drops of ink, he changed everything.

He looked at blood: cells. At muscle: cells. At skin: cells. But in the brain… the world’s leading scientists could only see a vast, tangled cobweb. Cajal rebelled. The most extraordinary organ had to be made of extraordinary cells. They just had to be found. And so, he worked from sunrise to sunset until he succeeded. There, hidden from the eyes of the rest of humanity, he discovered the universe of the mind, inhabited by independent cells: "the butterflies of the soul."