***This comment may contain Spoilers***
"Picnic na obochine" aka "Roadside Picnic written by the most popular among the Soviet readers of many generations writers in the genre of Science Fiction, brothers Arkadiy and Boris Strugatsky is much more than science fiction. It can be viewed as dark satire and anti-utopia as well. What is important, it is a very well written book which I've read many times and will read again.
The alliens have briefly visited Earth (perhaps for an emegency stop or for a picnic as the title suggests) and left behind many strange and unusual items, some of them funny and useful, some - dangerous and even deadly. These items became so popular on a black market that many people were ready to pay a lot of money or to risque their lives for them. The most desirable and mysterious of all was "Golden Sphere" that could grant any wish but nobody ever was able to reach it. Among stalkers, the persons possessing knoweledge of the area and its dangers, there was Roderick (Red) Schuhart, the main character of the book, He was not a saint; he was a human being with a lot of weaknesses. Red possessed inhuman intuition and luck that had helped him to survive the multiple trips to the Zone. But the Zone caught up with him in the end, and he was paying the ultimate price watching how his only child who was born as a beautiful and joyful girl was turning into the strange and mute animal. That was why Red decided to make the last trip to the Zone and find the legendary Golden Sphere. Red knew he could not go alone because just when you thought that you reached the Sphere there was an ultimate trap that could only be fed by a human being. Such great and desperate was Red's desire to get his daughter back that he took with him an innocent young man, teenager really, perfectly knowing that the man will never return from the Zone. Red found out that after he finally reached the Sphere, he did not know what and how to ask; his only hope was that the magic tool would reach inside his soul and find that his soul was still alive and bleeding from pain and begging for his daughter and for forgiveness.
Andrei Tarkovsky took the final chapter of the book and used the idea of the last trip for the film "Stalker" He himself along with the Strugatsky Brothers had rewritten the screenplay many times until he was satisfied with it. As much as I respect Tarkovsky and admire his films, I am not a fan of "Stalker" and I'd prefer if he had adapted the final chapter the way Strugatsky Brothers wrote it. I found the last chapter of the book much more interesting, deeper, and tragic than all the debates among the characters and monologues of the Stalker and his wife in the film.