What happens to men when they become fathers? How do men change psychologically and physically during pregnancy, birth and the first years of having children? In this film we go on a journey of discovery and ask brain researchers, geneticists, sociologists and psychologists. And we accompany three men during their adventure of becoming a father. Fathers are special: they belong to the rare 5% of all male mammals that take care of their offspring. Nature has specially equipped them for this, because they go through crucial changes when their children are born. Nevertheless, scientific research has so far mainly focused on mothers. But researchers have now begun to study the effects of fatherhood on both fathers themselves and their children. Similar to mothers, fathers are physiologically and hormonally altered by pregnancy, childbirth and childcare. For example, an expectant father’s levels of the “love hormone” oxytocin increase significantly, as this is nature’s way of helping him to develop positive feelings for his child. In addition, at birth his testosterone levels drop dramatically, which increases his sensitivity. We visit scientists around the world in their research facilities and laboratories and show the amazing results of their studies. We also follow three fathers in Germany, France and Sweden from pregnancy to infancy. In this way, we weave exciting science and personal stories into a fascinating film about the phenomenon of becoming a father and being a father.