Saffron's father has been grouchy since her mother died of fever after they moved to the Seaweed Slum. Life there could send anyone of the cliff edge, but Dad is all Saffron has in the world and she prays to Infinity the patrols won't catch him when he sneaks off on his secret missions. Dad was an astronautics engineer in his heyday, and his obsession with space junk gives metal fatigue a whole new meaning. At least she has her puppy, Nigel, for company.
Hippie Hermione scrapes by with her quack medicine and her stinky meat pies, but Saffron has ambitions. She will qualify as an herbalist and make fab cosmetics for the rich people in Server City. Hermione offers to coach Saffron for the exam, but Hermione's methods don't ring true. Her strawberry dreadlocks, black fingernails and pothead lifestyle are vile, and her recipes stink like rancid rats tails.
Sophisticated Marianne, the master herbalist, is the new neighbour. Dad invites her to tea, but for Saffron it's a disaster. First Marianne steals Nigel's heart and he squirms round her ankles like a pole dancer; then tells Saffron she won't pass her exam. Saffron's father has absolutely no resistance to the woman's charms. Their cosy hearts-and-flowers club leaves Saffron out in the cold. Dad and Marianne? At their age? It's disgusting.
Nate, the student astrophysicist, seeks the engineer's help with his space probe, snagged on a defunct satellite in the junk orbit, but the authorities hear of it and the three must flee to the Astro Station. When it's too dangerous, Dad sends her back to the slum for safety, but he's arranged for her to stay at predatory Marianne's; the last place in the universe Saffron wants to be.
Dad and Nate are arrested, and Marianne and Saffron venture into the deadly city to discover what they can, but the plan goes wrong. If Saffron wants to see Nate and her father alive again, first she must survive the dangers of the city and find them.