Plot summary
Grand Nagus Zek, the "financial leader" of the Ferengi race and Quark's idol, arrives on the station and shows Quark and Rom his new project: he has rewritten the Rules of Acquisition, the sacred business proverbs by which the Ferengi live. In the new book, Zek encourages Ferengi everywhere to renounce selfishness and greed and become kind and giving. Zek now wants to lead a life of altruism and wants Quark and Rom to run his charitable foundation. This horrifies Quark, because profiteering lies at the heart of Ferengi identity, and the Grand Nagus is supposed to be the paragon. Quark warns Rom that other Ferengi will violently depose the Nagus if he tries to change the Ferengi way of life.
Doctor Bashir can find no sign of mental or physical illness in Zek, and his uncharacteristic behavior does not appear to be a ruse. Wanting answers, Quark and Rom break into Zek's shuttle and discover an Orb of the Prophets, which Zek is planning to give to the Bajorans. When Quark is exposed to the Orb, he has a vision in which Zek describes the New Rules of Acquisition as a "gift". Quark deduces that Zek visited the wormhole and contacted the Prophets so that he could use their knowledge of the future for profit, and that they are responsible for Zek's transformation.
Quark forcibly takes Zek back to the wormhole to ask the Prophets what they did to him. The Prophets, being immaterial creatures who do not experience time linearly, found Zek's obsession with accumulation of material wealth to be strange and adversarial. They "de-evolved" him to a more primitive state, resembling the less greedy ancestors of the Ferengi. They threaten to de-evolve Quark as well, but Quark warns them that if he is also changed, more curious Ferengi will visit the wormhole looking for answers. Because the Prophets like their privacy and find Ferengi annoying, they release Quark and restore Zek to normal.
Zek dismantles his charitable foundation and has all copies of the New Rules of Acquisition destroyed. After Zek leaves, Rom confides that he embezzled money from Zek's foundation, which delights and impresses Quark.
A subplot involves Bashir being nominated for a medical award which he ends up not winning. Bashir feigns nonchalance, but inside he is seething.
Credits
Adapted from Wikipedia contributors, Prophet Motive. Paragraphs and formatting adjusted; illustrations, reference markers, block quotations and non-story material omitted.