Bertrum Boltwood is one of the near forgotten heroes of the pioneering days of radioactivity. Boltwood was an analytical and physical chemist, at Yale and in private practice, who specialised in analysis of ores containing rare earths, and with uranium and thorium which are commonly associated with rare earth minerals.

The book covers from 1904 until 1927, when Boltwood regretably committed suicide. This collaboration was that of equals, two men with great respect for each other's work and who enjoyed each others company whenever they could.  Boltwood, a year older than Rutherford, did meticulous work in separating the radioactive elements from ores and each other. He made an impressive contribution to the chemical processes needed, in identifying "missing" elements in decay series, in supplying Rutherford with various separated and purified radioactive samples and in dating the age of minerals. Being good friends, they exchanged gossip and frank discussions about other workers in the field. After Rutherford returned to England, Boltwood often spent the summers in Rutherford's lab so they had a great pool of mutual friends to keep each other in touch with.