The Door into Summer is a science fiction novel by Robert A. Heinlein, originally serialized in The Magazine of Fantasy & Science Fiction (October, November, December 1956, with covers and interior illustrations by Frank Kelly Freas) and published in hardcover in 1957. It is a fast-paced hard science fiction novel, with a key fantastic element, and romantic elements. In three separate Locus Magazine readers polls from 1975 to 1998, it was judged the 36th, the 29th, or the 43rd all-time best science-fiction novel.
The title was triggered by a remark that Heinlein's wife had made: in the novel, the protagonist's cat refuses to leave their house through any of its numerous doors when he sees snow on the ground: he is looking for The Door into Summer. Heinlein wrote the complete novel in only 13 days. No rewrite was needed, only some light editing that Heinlein did himself.
Hired Girl, Inc. manufactures robot vacuum cleaners, but Dan had been developing a new line of all-purpose household robots, Flexible Frank, when Miles announces his intention to sell the company (and Frank) to a large corporation in which Miles would become a vice-president. Wishing to stay independent, Dan opposes the takeover, but is outvoted and then fired as Chief Engineer. Left with a large financial settlement, and his remaining Hired Girl stock, he elects to take "cold sleep" (suspended animation) with his beloved pet cat "Pete", hoping to wake up thirty years later to a brighter future. He negotiates a contract with an insurance company to handle his finances, but then during a medical examination the doctor notices that Dan is drunk, gives him an injection and a drink of medicine to sober him up, and a warning not to come back drunk if he still wants the sleep.
His mind clear, Dan decides instead to mount a counter-attack. First he mails his Hired Girl stock certificate to the one person he trusts, Miles' stepdaughter Frederica "Ricky" Gentry. Dan confronts Miles and finds Belle in Miles' home. Deducing that they are married, he begins to pick apart their scheme, but before he can leave to start an investigation, Belle injects him with a drug, reducing him to somnolent compliance. Belle announces that he knows too much and must be disposed of. Miles has no stomach for violence, but they discover Dan's plans to go into cold sleep. Belle, an accomplished forger, is able to alter Dan's commitment documents to have him placed in a repository run by her cronies — a subsidiary of Mannix, the company that was trying to buy Hired Girl, Inc.
Dan wakes up in the year 2000, with no money to his name, and no idea how to find the people he once knew. What little money Belle let him keep went with the collapse of Mannix in 1987. He has lost Pete the cat, who fled Miles' house after Dan was drugged, and has no idea how to find a now middle aged Ricky.
Dan begins rebuilding his life. He persuades Geary Manufacturing, which now owns Hired Girl, to take him on as a figurehead. He discovers that Miles died in 1972, while Belle is a shrill and gin-sodden wreck. He reluctantly meets her to glean what she knows about Ricky, but all she recalls is that Ricky went to live with her grandmother about the time Dan went into cold sleep. Her scheme with Miles collapsed, as Flexible Frank disappeared the same night she shanghaied Dan. She blames him, although Dan has no idea who might have stolen the prototype. Oddly, Flexible Frank is everywhere in the future, acting as hospital orderly, bellhop, and a thousand other menial jobs once filled by people. It is called Eager Beaver, made by a company called "Aladdin Auto-engineering," but Dan knows his own work. Someone has taken his prototype and developed it. Another ubiquitous device is Drafting Dan, a machine which replaces the manual drafting table with a display driven by a keyboard. Dan remembers that this machine was only an idea when he took the sleep. He is even more baffled to find that the primary patents for both devices are credited to a "D. B. Davis."
His buddy Chuck at Geary persuades him it's just a coincidence, but over a few beers Dan starts joking about going back in time. Chuck lets slip that he once saw time travel working, in a lab in Colorado. Dan is set to go and find out what this means, but Chuck persuades him to relax and do some more checking first.
At that point Dan finds that Ricky has been awoken from cold sleep and left Los Angeles for Brawley, California. Dan tracks her to Yuma, Arizona, where she was apparently married. When Dan looks at the marriage register, he immediately empties his bank account and heads for Colorado.
In Boulder, he befriends Dr. Twitchell, a once-brilliant scientist reduced to drinking away his frustrations. Eventually, just as Chuck had told him, Twitchell admits to having created a time machine of sorts. He can send two equal masses in opposite directions in time, but cannot control which one goes into the past, and which into the future. Pretending to be writing a book about Twitchell, Dan persuades him to set up a dry run for thirty-one years with him as one of the masses. With the machine powered up, Dan goads Twitchell into throwing the switch and finds himself falling. Picking himself up, he is confronted by a man and his wife. Any hope of guessing the year from their clothes is frustrated by the fact that both are naked. He fears that this is some futuristic fashion change, until he realizes he's reappeared in a Nudist Colony.
Fortunately, Dan has gone back to 1970, some months before his confrontation with Miles and Belle. Dan is befriended by naturists John and Jenny Sutton and persuades them to help him in his mission. His plans, among other things, include creating Eager Beaver and Drafting Dan, and then taking the cold sleep he originally planned. He has brought back gold worth $20,000 in 1970. With John's assistance in converting suspect gold to cash, Dan is able to set up a machine shop.
Working rapidly, Dan creates Drafting Dan, which he then uses to design Protean Pete, the first version of Eager Beaver. Leaving John and Jenny to set up a new corporation to be called "Aladdin Auto-engineering," he returns to Los Angeles, and stakes out Miles' house on the fateful night. Watching himself arrive, he lets events unfold until Pete the cat emerges, then takes his own car and uses it to remove Flexible Frank and all his engineering drawings from Miles's garage.
Destroying the drawings and scattering machine parts across the landscape, he heads out to meet Ricky at her Girl Scout summer camp. There he tells her where he is going, and over her protests tells her that the Hired Girl stock he is giving her will make her rich enough to take the cold sleep when she is old enough, if she still wants to join him in the future. Ricky is remarkably mature for her age, and asks Dan if he is doing this so they can get married. Dan tells her she is correct.
He sells his car for quick cash, enough to get him to his cold sleep appointment, made a few days ago, or six months ago, or thirty years ago, depending on your point of view. With Pete in his arms, he sleeps for the second time.
In 2001, he awakes to a note from a much older John Sutton, along with a substantial amount of money. He greets Ricky, now a twenty-something beauty, when she awakes. They leave for Brawley to retrieve her possessions from storage, and then are married in Yuma. Setting himself up as an independent inventor, the way he likes it, he uses Ricky's Hired Girl stock to make changes at Geary, settling back to watch the healthy competition with Aladdin. At the end Ricky is pregnant, and Dan's personal Door into Summer has been well and truly found.
Miles Gentry is Dan's former Army buddy and business partner, handling the financial and legal side. By marrying a widow, Ricky's mother, who subsequently died, he became Ricky's de facto guardian. After Dan's mother and sister died in the war, the three, with Pete, became a small family with Ricky running the household as well as any adult, while Miles and Dan put Hired Girl, Inc. together. However neither can resist the charms of Belle Darkin.
Belle S. Darkin presents herself to Miles and Dan when they most need help with the company. She is a brilliant secretary, book-keeper and office manager who is willing to work for a pittance. Separately seducing the two men, she conspires with Miles to oust Dan by having him sign documents he has no time to read. These make him legally an employee of the company so he can be fired. At the same time she persuades him to give her a share of the stock, as a betrothal gift. This is sufficient, with Miles's share, to outvote Dan. When later Dan has her investigated, a life of crime is revealed involving multiple marriages, financial scams, forgery, and even minor vice crimes. Dan arranges for this information to be revealed when Miles dies, cutting Belle out of his estate.
Frederica Virginia "Ricky" Heinicke is physically an 11-year-old girl but emotionally almost adult. We see little enough of her in the novel, but she is certainly the object of Dan's quest. Like all Heinlein's heroines from this period, she is an intelligent red-head, and clearly modeled on Virginia Heinlein, even having a version of her name and her childhood nickname, Rikki-Tikki-Tavi. Ricky's last name is that of her paternal grandmother in Brawley, California, although in the beginning she uses "Gentry." This causes Dan difficulty in locating her, as he only knows her by that name. Miles never formally adopted Ricky, so she is able to disappear into the household of her only living blood relative, preventing Belle and Miles from depriving her of Dan's gift of Hired Girl stock.
Petronius the Arbiter or Pete, Dan's cat, is an under-appreciated character in the novel. Highly vocal with a wide range of expressive sounds, he acts as a sounding board for Dan's ruminations and fulminations. He goes everywhere with Dan, carried around in an overnight bag, emerging when Dan orders him a ginger-ale in a bar, or buys him food at drive-in restaurants. When Dan is drugged by Belle, Pete yowls in ever higher levels of distress, finally reaching the awful keening of feline despair that chills the blood. Miles and Belle commit the fatal error of trying to manhandle Pete out of the house, and he makes them pay, switching to his war cry. In this state even Dan, visiting from the future, must bide his time before attempting to take Pete with him to safety. Later Pete is Dan's passport to Ricky, the Girl Scout camp leader being another "cat person."
Chuck Freudenberg is Dan's "beer buddy" and best friend at Geary Manufacturing, and one of the few "real" engineers employed by the company, which has ceased to innovate. He listens to Dan's ideas for new devices, warning him to keep them to himself lest Geary declare them company property. While in college he witnessed Dr. Twitchell's time travel experiments, providing Dan with the opportunity to return to 1970. On his return, Dan uses his voting stock from Hired Girl, Inc. to rearrange Geary, promoting Chuck to Chief Engineer.
Dr. Hubert Twitchell is a brilliant physicist at the University of Colorado at Boulder, who invents time-travel while studying antigravity, only to see his work declared top secret by an armchair colonel looking for promotion to General, robbing Twitchell of a Nobel Prize. He descends into drink and self-pity for the rest of his life. Dan eventually contacts him after his second awakening in 2001, and promises to follow through with telling Twitchell's story in a book.
The critic Alexei Panshin, however, had a much more favorable view of the book. Writing in 1968, he says that "as a whole, the story is thoroughly melodramatic but very good fun. I imagine that it was a very enjoyable story for Heinlein to write, particularly the nicely-developed engineering ideas. It was as though Heinlein the engineer said, 'If I had the parts available, what little gadgets would I most enjoy building?' and then went ahead and built them fictionally. A good story."
More importantly from Blish's point of view is Heinlein's treatment in the book of time travel: "Every other important subject of science fiction which Heinlein has examined at length has come out remade, vitalized and made the author's own property. It didn't happen here, for the first time in Heinlein's long and distinguished career — and not because Heinlein didn't have something to say, but because he failed to embody it in a real protagonist. Evidently, Heinlein as his own hero is about played out."
Panshin also demurs on the time-travel issue. He writes that "time travel stories are generally so complicated that they have to be tightly plotted if they are to be successful, and Heinlein's time travel stories as a group are probably his best constructed. This one is no exception."
At the time, science fiction was attempting to shake off its pulp magazine image and acquire some legitimacy as a literary form. Thus Blish, who was then writing the first part of his own high-concept series, After Such Knowledge, might have seen a quickly written novel such as this as a step backward.