Manifold: Origin is the third part of the series, and like the rest can be treated as a standalone novel. However, unlike the other two novels (Time and Space), it does offer the reader something of an overall conclusion.
Reid Malenfant and his wife Emma are finishing off an African tour for NASA, when the moon is replaced by a much larger object, one with an atmosphere and obvious signs of life. In shades of Fritz Leiber's The Wanderer everything starts to go to hell in a hand basket, as the massive object's tides disrupt geology and weather all over the world.
Meanwhile, a mysterious blue ring is dropping hominids over the Olduvai Gorge, and eating aeroplanes. Among those swallowed is Emma, leaving Malenfant to deal with The Tide, and to plot a journey to the Red Moon. On its vast red plains, Emma has found that a thriving ecology of hominids - hominids that appear to have come many different versions of the Earth. As Malenfant struggles to encourage NASA to mount a mission to the Red Moon, Emma is trying to survive a hostile new world. And what if the Red Moon moves on again?
Baxter's writing here is some of his most lyrical, as he describes the landscapes of the Red Moon. But he does much more, as he attempts to describe the alternate states of conciousness of the various hominid species - from idiot savant's with no memory, to advanced hominids with much faster perceptions. With so many very different viewpoints, Origin could be a difficult novel to read, but Baxter's able to guide the reader through his story, pulling us to a complex conclusion that promises to explain just what the Manifold is...
Origin is a fitting conclusion to some of the best modern British SF around.