The authors are unequivocal in their conclusion, which is presented in the preface: "...recent forensic analysis of remnants of [Brahe's] hair reveals that he was murdered, systematically poisoned. And all the answers as to motive, means, and opportunity point directly to one suspect: Johannes Kepler."
The book provides a detailed presentation of Brahe's life and work, and the relevant aspects of Kepler's. I won't reiterate the evidence here, but I will instead insert a few of the "things I learned" from the book.
Since we accept a heliocentric solar system, it's sometimes hard to understand how pre-Copernican scholars could have been so accepting of a geocentric model, but this analogy from the book is quite informative in that regard:
"It's important to understand in all of this that, visually and mathematically speaking, there is no differnce between a moving earth revolving around a stationary sun and a moving sun revolving around a stationary earth... a demonstration is provided by those battery-powered models of the solar system sold at planetariums and most toy stores. Pick it up by the sun and hold that stationary, and all the planets will revolve as they are supposed to. But if you hold the mechanism up by the earth and hold that stationary, all the planets and now the sun, too will continue to revolve, in exactly the same relation to one another as before." (pp. 83-4)This sentence startled me:
"Apparently, Rudolf [Holy Roman Emperor Rudolf II] had been peeking through his window as Brahe approached in his carriage, and -- fascinated as he was by all things mechanical -- was especially interested in an odometer he saw affixed by the wheel. Brahe had it brought to him, and after examining it carefully, Rudolf said he would have one made by his artisans according to the same pattern." (p. 137)Odometers in the 16th century?? Who knew? Topic bookmarked for a future separate post. Here's more about Rudolf:
"More a collector than a connoisseur, with tastes that were less eclectic than simply promiscuous, Rudolf sent his agents across Europe to purchase items that might excite his fancy. Some brought back Durers and Breugels, while others transported back objects by the thousands whose major organizing theme seems to have been their oddity. All were placed in his famous Kunstkammer - the private rooms in which he would increasingly shut himself off - which contained what was perhaps the largest private collection up until that time.There is a painting of Rudolf and a diagram of his family tree in the post below this one.
There, housed in myriad cabinets and displayed along tabletopes, lay thousands of disparate artifacts: beautiful porcelain cameos along with the shells of tortoises, crabs, and other sea creatures; the horn of a unicorn (which probably came from a narwhal) and rhinoceros horns mounted in gold; priceless gems; drawersful of gold, silver, and copper antique medals; as well as the dagger with which Caesar's wife was said to have been murdered and a knife swallowed by a Prague peasant. Mechanical objects were a special fascination: among the many clocks, globes, and astrolabes, records mention a mechanical peacock that walked, turned around, and fanned its featuers and a windup spider that could scurry across a table..." (p. 143)
Chapter 15 of the book is particularly good in explaining the strained relations between the two scientists and the consequent motivation for murder. Chapter 22 details the use of mercury as a medication and the formulations of it that the (al)chemists of the time created, which were of quite varying potency and toxicity. In explaining why Brahe's acute renal failure was probably not due to a bladder stone, the authors point to the absence of any attempts at catheterization, which would have been attempted had anuria been accompanied by a distended bladder:
Jessenius, one of the leading medical authorities of his time, wrote in some detail about urinary problems and their cures. He clearly had considerable experience in the area and recommended in one of his numerous publications "the small tubes, conceived by Venetian wound doctors, which are made of horn and made flexible by soaking them in warm water," rather than the "slim wax light used by Fabricius Aquapente (which he warms up and then inserts coated with almond oil)," as the latter were "not strong enough to overcome the resistance of the bladder opening or a bladder stone." (p. 213)A surprising sophistication in knowledge of urinary catheters - before the invention of plastic or the discovery of rubber. Since Brahe had access not only to physicians but to the physicians of the royal family, the fact that catheterization was not considered is prima facie evidence that the physicians attending him considered the acute renal failure to be nonobstructive in nature (or at least above the bladder). That, along with the mercury in the forensic analysis of his hair, constitutes the principal evidence of murder by poisoning.