In a secretive chamber, technicians worked on a machine called the Dip, which was capable of dredging the future. Hasten, an expert from Histo-Research, was brought in to help them with a problem they had encountered.
They had used the Dip to photograph the future, and at first, everything seemed fine. However, when they revisited a period they had already photographed, they found that everything had changed for the worse. War and destruction were everywhere, and eventually, there were no human beings left, only empty cities functioning mechanically. Wood, the head of the Department, revealed to Hasten the secret purpose of the Department's Time Dip, which was to explore the future instead of the past.
This Dip is set, not for antiquity, but — for the future.
Hasten was sent into the future using a Time Car to find out what had caused the lethal factor that wiped out humanity.
You’re going, the most competent person available.
He arrived in a meadow with cows and butterflies, and as he explored the area, he was stung by a butterfly, causing his hand to become black and swollen. He continued his journey and found a city with a library, where he collected books and newspapers to bring back with him.
As he returned to the Time Car, he noticed that the butterflies had become more aggressive and intelligent, carrying tools and cutting their way into the Time Car. Hasten managed to escape back to his own time and reported his findings. The lethal factor was a form of toxic life that attacked only human beings - the butterflies. They were intelligent, planning attacks, and possibly rapidly breeding and adapting.
Corrosive secretion? He smiled grimly.
Hasten's discovery prompted an emergency session of the Council to organize units all over the planet to combat the butterflies. However, upon inspecting the Time Car after his return, Hasten discovered cocoons on the hull, indicating that the lethal butterflies had already made their way to his time.