World War I pilot Terry Decker flies through a white cloud and emerges 42 years later, landing at an American Air Force Base in France, at which point he proves that a Nieuport 28 biplane is capable of doing a causal loop just as well as he can do an Immelmann Turn.

The title suggests that Professor Amos Shute’s intrepid travelers are going back in time to four planets that are identical in every way to our own, but then again, perhaps those four planets were merely at earlier times to begin with. We won’t say one way or another, but we are glad that the Spanish Flu pandemic, World War I, World War II, and World War III were all averted on some Earth.

Dick, a composer, and his boyhood friend John, now an eminent scientist, find themselves in a patchwork world of different times from classical Greece to a far future that humanity barely survives.

My favorable impression is no doubt reflective of the time when I read it (the summer of 1970, nearly 13, while moving from Washington State to Alabama). Perhaps the fiction doesn’t hold up as well decades later up, but the issues of time that it brings up still interest me and it was my first exposure to the idea of a geographic timeslip. And, similar to Asimov, Hoyle served to cultivate my interest in the natural sciences.

Two young, boarding-school students—Charlotte in 1963 and Clare in 1918—swap minds through time every night, until one day the bed that’s causing all this magic gets moved to the hospital ward, and they are stuck in each other’s times.

Finney’s sequel to Time and Again initially finds Si Morley living a happy life in the 19th century with his 19th century family, while The Project in the future never even got started because he prevented the inventor’s parents from ever meeting. But vague memories linger in some of the Project member’s minds, and Morley can’t stay put.

In the year 2035, with the world devastated by an artificially engineered plague, convict James Cole is sent back in time to gather information about the plague’s origin so the scientists can figure out how to fight it.

In one instantiation of her life, Ursula Todd dies just moments after her birth in 1910. Fortunately (for the sake of the novel), time seems to be cyclic, so she and the rest of the world get many chances at life. At times, she partially recalls her other lives, resulting in many consequences to history and her personal development.

Fresh from finishing her Ph.D., Madeline Maxwell (aka Max) runs into her high school mentor who encourages her to apply for a position with a cloistered group of historians called St. Mary’s Institute of Historical Research.

Of the 43 children born 1 October 1989 with no gestation period, the eccentric and sometimes cruel billionaire Reginald Hargreeves brought up seven of them and turned them into the super-powered group called the Umbrella Academy when they developed powers. Nearly thirty years later, after Hargreeves dies, the five surviving members of the group gather at their family home. Oh, and: Number Six died some time ago and only Number Four can see him; Number Five disappeared about seventeen years ago, but he’s back (and in his 13-year-old body) after living 45 years in a post-apocalyptic future that’s scheduled to start in eight days.