This was a really fun read, and definitely sucked me in, but Simak has written better. There were at least 1 or 2 completely gratuitous scenes in it, and the back-cover-blurb is laugh out loud TERRIBLE and will make people think you're reading utter trash. It's not high literature, but it's better than what you'd think based on that and the cover art alone!
(Back Cover Blurb being:
"A high-pitched, ragged screech came from behind the house, a caterwaul of fright. Boone started running toward the sound. But as he was rounding the corner, something going fast and hard struck him in mid-stride, tumbling him nose down into the soft dirt.
He pawed at his face to wipe off the dirt and pulled himself to his feet. Emma was streaking for the traveler, with the others close behind. It was Emma, he thought, who had knocked him down.
Then he saw what was chasing them. It was like a living spider web, more than twelve feet across, with pulses of energy throbbing across the tiny threads of the web. Behind the threads was a disk of some sort that might have been an eye. And he saw mechanical appendages... things like arms were already reaching out for him.
Enid's voice shrieked at him. 'Boone, you fool! Run! It's a killer monster!'")
A good read. I wish Simak had continued this story as a series.
Simak has written another clever, intriguing, and thoroughly enjoyable book. The mystery of the time travelers, the intrigue of Hat, and the interfering aliens all make for a great ride.
Clifford Simak was renowned as one of the "pastoral" Sci Fi writers, used upon his creation of stories of basically good, unheroic characters who inadvertently and unexpectedly find themselves in an out-worldish situation that appear threatening but may not be -- or indeed may be. Watching these situations evolve and resolve can be fascinating reading. This novel was one of Simak's last and ends on a positive note about the future.