Not quite the end of the adventures of David Falkayn and Nicholas van Rijn. But close. It may even be their descendents that carry on the tales, though I don't recall exactly. I do know that this has a lot of allusions to earlier tales of theirs.
But it opens with the discovery of the title planet. Rediscovery, actually. Intelligent beings are mining it for the super-elements that it contains, spawned by a long ago supernova. This means trouble. The companies of the far future have fallen, on the whole, into two groups: the Home Companies, doing crony capitalism but good on Earth, and the Seven in Space that ignore them. Nicholas van Rijn leads one of the diminishing independents.
It brushes on the story of Sandra (from The Man Who Counts) and her adventures after having van Rijn's son and leading to her becoming the Grand Duchess. And then trouble strikes. The Baburites, hydrogen-breathing aliens, demand control of Mirkheim. Sandra's efforts to claim it for Hermes to protect the original entrepreneurs causes conflict and the occupation of her planet. Back on Earth, van Rijn reassembles David Falkayn, Adzel, and Chee Lan to look into things -- even though Falkayn left after his first child was born, this is too important.
It involves the questions of how the Baburites built their navy so well, escaping with news, trying to take a captive, rescuing the miners from Mirkheim, van Rijn's son meeting him, and much more.