The Strugatskys posit that the Earth experiences a brief visit from extraterrestrials, who leave behind them - well, call it litter, such as might be left by you and me (in one of our less socially conscious moments) after a roadside picnic. The nature of these discards, products of an utterly alien technology, defies most earthly logic, to say nothing of earthly analytical science, and their potential is limitless. Warp these potentials into all-too-human goals - the quest for pure knowledge for its own sake, the search for new devices, new techniques, to achieve new heights in human well-being; the striving for profit, with its associated competitiveness; and the ravenous thirst for new and more terrible weapons - and you have the framework of this amazing short novel. Add the Strugatskys' deft and supple handling of loyalty and greed, of friendship and love, of despair and frustration and loneliness, and you have a truly superb tale, ending most poignantly in what can only be called a blessing. You won't forget it.