Given the huge success of China Mieville's second novel Perdido Street Station, a follow-up was eagerly expected, but Mieville has bucked expectation by setting The Scar in an entirely different area of Bas-Lag - as such readers hoping for a return journey to the vivid city of New Crobuzon will be disappointed, though to be fair having explored it so thoroughly already any follow-up utilising the same setting may well have suffered from diminishing returns. Instead The Scar is set almost entirely on the floating city state of Armada - a pirate city that is comprised of a mass of stolen ships lashed together, and follows the fortunes of two shanghaied inhabitants: one of whom is desperate to escape, and the other who having been rescued from a prison ship finds a haven on Armarda.
As such, The Scar is the best sort of sequel, in that it is only tangentially linked to the previous novel - in this instance the lead heroine is initially on the run from New Crobuzon because she is wrongly suspected of being involved with the Slake Moth outbreak that drove Perdido Street Station. However, while you don't therefore NEED to have read Perdido Street Station in order to enjoy The Scar, I would still recommend reading the previous volume first for one simple reason - it's slightly better.
The Scar is filled with fantastic concepts -the city of Armada itself; the leviathan avanc that the Armadan's plan to harness to their city; an island of terrifying mosquito women; and a scar in the fabric of Bas-Lag seemingly created by a crashed alien spaceship that bleeds out quantum instability, and the characters are compelling, but the crucial difference between The Scar and Perdido Street Station is the lack of narrative tension this time round. In Perdido Street Station the narrative was driven by the deadly threat of the Slake Moths, and the characters desperate attempts to contain the threat before the creatures spawned - in The Scar the threat is much more nebulous - whether it's the threat of the monstrous Grindylow hunting someone on board Armada, or the Lover's quest to drive Armarda into the Scar, the threat's are always somewhere over the horizon, and during the novels middle section the book feels rather becalmed. As with Perdido Street Station this is a brick of a novel - unlike Perdido Street Station this feels in need of a little editing.
Still - a fine book, but one it's easier to admire than love.