This is a relatively early work for Heinlein, having first been published in 1957. More famous works such as “Stranger in a Strange Land” are still ahead of him. As such, this book, while quite good, is not great.

The story concerns protagonist Dan Davis, an inventor who is cheated out of his life’s work, and wants to gain revenge, as well as finding some new meaning in his life. Time travel, via cryogenic sleep into the future, and via a time machine back again, helps him achieve what he wants.

As a cat lover, I first must say how very much I enjoyed the character of Pete, the protagonist’s cat. The story’s name comes from the cat wanting to check all the doors of the house during winter, looking for the door into summer. The hero at he start of the story states that he, like his cat, is looking for his own door into summer and away from the ‘winter’ his friend and fiancé have left him in by their betrayal. (I actually have personal experience of this type of cat behaviour. A cat I used to have, Figaro, on finding rain outside the front door, would immediately go to the back door. She would them meow at me insistently, apparently under the impression I could do something about the rain.) Pete the cat is great fun. He rides around in a bag with his owner, responds to conversations with meows, and takes on the bad guys when they attack his owner. This is a great character who is still a cat.

He had a fixed conviction that at least one of them must lead into summer weather. Each time this meant that I had to go around with him to each of eleven doors, hold it open while he satisfied himself that it was winter out that way, too, then go on to the next door, while his criticisms of my mismanagement grew more bitter with each disappointment.

Dan Davis is smart, cocky, but at the same time a bit clueless. He allows himself to be totally conned by a femme fatale type woman. Dan is okay as a character. I found him a little too full of himself, even after making some rather silly mistakes. He doesn’t come across as being as smart as he thinks  he is. He is a bit of a cliché in that respect – the inventor who can’t be bothered with the business side, so gets conned by his business manager and girlfriend. This is not an original idea even in the fifties.

The femme fatale, Belle, is something of a problem. She is obviously skilled in fraud and deception. She is the only female character with any real presence in the story. But she represents a common thread n Heinlein’s work that is a bit hard to deal with from a modern perspective. She is a one-dimensional representation of Heinlein’s sexism. He was a product of his time, and I have not yet read any of his works where this sexist attitude is not present in some capacity. The hero even absolves his friend of some of the guilt by pitying him for being conned in the same way. He essentially puts all the blame on Belle, who has ‘lured’ the partner into abetting her. What little is mentioned about women in general does not consider them in any other capacity than as home-makers. It’s not a big aspect of the book, so you just need to be aware that it’s an old book with old ideas.

Chuck had a theory that women were closely related to machinery, but utterly unpredictable by logic. He drew graphs on the table top in beer to prove his thesis.

World-building in this book had aspects of interest, but seemed incomplete, so it was hard to picture the environment in either time period. I think this was often because Heinlein mentions things to give you a hint of what he’s referring to, but doesn’t build on it enough for a real picture to be envisaged. It is almost laughable to hear him mention a ‘six week war’, supposedly an atomic conflict, which doesn’t seem to have caused the world much damage. It seems ludicrous to us that he would not understand the devastating consequences, should a real atomic war occur. However it would not be the first work, either story or film, of that time, that massively underestimated what nuclear war could do. I don’t think people really understood the dangers of radiation or the length of time it lasted. The scientific community may have, but the general layperson did not. it would not be til the sixties and seventies that literature represented the horrors of nuclear war in a more realistic way.

Time travel and its potential paradoxes play an important role in this story. The main character jumps forward thirty years, then back thirty years, then forward thirty years. This creates at one point a sequence of events that we already know from inside the house, now being observed from outside the house, as the character is in two places at once. Events that were previously unexplained now become clear as it is the second Dan who takes these actions. It’s an old time travel trope, and it’s fine as far as it goes. I felt it was a bit too pat, in that Dan moved into the actions that he needed to do way too easily. There was no moment when he stopped and tried to remember what he’d been told or overheard the first time, in order to make sense of the actions he now needed to take. It felt a little too smooth. He in fact has a short moment of wondering about the sequence of events but only at the end of the story. There should have been a bit more hesitation and confusion while it was happening.

Nothing could go wrong because nothing had…I meant “nothing would.” No – Then I quit trying to phrase it, realizing that if time travel ever became widespread, English grammar was going to have to add a whole new set of tenses to describe reflexive situations – conjugations that would make the French literary tenses and the Latin historical tenses look simple.

The biggest oddity about this book lies in the character of Rikki. She is a child, the step-daughter of Dan’s business partner, and he is fond of her. There is no indication of anything creepy, until right near the end, where he suggests she go into cryogenic sleep to catch up with him in the future, and then they will get married. Opinions vary on this. Some people decry this as being perverted and creepy, others point out that he didn’t behave badly towards her as a child. I honestly am not sure where I stand on this. It startled me when it got to that point. I had not expected it. But it is true he never behaved in a wrong way towards her when she was under age. One could say that they were soul mates who were born at the wrong times, I guess. This part of the story is quite a small one, and really doesn’t have much bearing on the plot. You could almost wonder if Heinlein isn’t guilty of shoehorning in a happy ending, however awkwardly.

Heinlein went on to write much better works than “The Door into Summer”. It has many flaws, as I’ve pointed out. It’s reasonably entertaining, however. I can recommend it for a bit of light reading.