The title of this assembly of stories is the translator's clever triple pun: an allusion to Othello, "mortal engines" are manmade, impermanent, and sometimes deadly machines--robots, to be exact. Included are all the tales from Lem's "Fables for Robots" and three other stories ("The Sanatorium of Dr. Vliperdius," "The Hunt," and "The Mask") that double the size of the book.
The fables are like--well, fables. That is, the prose style resembles Aesop or Andersen ("Once there lived..."); the narrative recounts long-ago events; and each tale presents a message--or, at least, a lesson for us humans disguised as a moral for them robots. These eleven shorts recall Borges (or even Poe) at his most playful, but read in sequence they tend to become a tad formulaic (several robots are sent on a mission; each fails, but the last one succeeds). And if you're a lover of science jokes, these stories will be your playground; Lem packs references to chemistry, physics, geology, computer science, and electronics--often in the same sentence: "self-motes came from distant lands, like the two Automatts, vector-victors in a hundred battles, or like Prostheseus, constructionist par excellence, who never went anywhere without two spark absorbers, one black, the other silver; and there was Arbitron Cosmoski, all built of protocrystals and svelte as a spire...."
If, like me, you prefer a little more story and a little less pun, you'll find that the gems of the book are the three bonus tracks. The last two, in particular, are among the best I've ever read by Lem, and have nothing in common with the fables other than the automaton theme. "The Hunt" is a rollicking adventure story featuring Lem's famous alter ego, Pirx the Pilot, on a mission to destroy a homicidal robot. "The Mask" may well be the best Lem story I've read: the haunting stream-of-consciousness of a robot who, like an otherworldly Tristram Shandy, narrates its own birth, consciousness, self-realization, metamorphosis, rebellion, and--above all--its futile pursuit of love. The opening pages have a deceptively languid pace, until the robot sheds its "mask" (in a surprisingly squeamish scene) and, during the ensuing chase, reveals its lethal assignment. These last stories are worth the price of the whole book.