They walked like men

I like Simak, but this seems to me an odd and untypical Simak novel. It was published in 1962, between [b:Time Is the Simplest Thing 1269436 Time Is the Simplest Thing Clifford D. Simak https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1263950437l/1269436.SY75.jpg 1426997] and [b:Way Station 190999 Way Station Clifford D. Simak https://i.gr-assets.com/images/S/compressed.photo.goodreads.com/books/1326490682l/190999.SY75.jpg 348798], which may be his best novels; but it's unlike either of them. I rather suspect (without evidence) that he drafted it much earlier and left it in a drawer for years before deciding to publish it in 1962.The hero is a very 1950s newspaperman (like Simak himself), who discovers that Earth is being quietly and secretly invaded and taken over by aliens who can disguise themselves as humans. There seems to be nothing he can do about it, until he discovers that they have a bizarre vulnerability.It's a highly improbable story, and it's not one that I actively enjoyed, although it's readable enough that I got all the way through it. Some people read and enjoy it as a comedy, but I find that difficult: what I see is another Simak hero who is lonely and puzzled and faced with major (if unlikely) problems.This time it's only the aliens who can do weird things. The hero remains an ordinary guy throughout, apparently alcoholic, with a rather tolerant girlfriend but no special powers.