Spacewrecked children unsnarl alien puzzle: Ginnela and Pete Wade are on their way to a new foster home and a new planet when their space ship is rammed as it leaves hyperspace. In the excitement, the two children are left aboard with dwindling supplies, a junior computer, and an inscrutable alien cargo ship. As a final blow, their game but feeble computer is taken over by the alien ship and can no longer give the children information. But Beethoven saves the day: a spirited recording of the Fifth Symphony stirs both their computer and the alien one to establish communication with the children, and they emerge from hyperspace as heroes. Excitement and anxiety build nicely here, and the two orphans thrown on their own--expected to be self-reliant but criticized by adults for their independence--are well drawn. This Asimov writes more smoothly than the other one, but does less playing with ideas; still, there are nice touches--such as a little computer that panics when severed from its larger host. There are also improbabilities--like the gift-wrapped alien ""toy"" that ensnares the ship--but by and large this is a cheerful, entertaining yarn.