Search units, which appeared as typical horror movie "zombies", were artificial creatures created by Leet to search for its life-shell. Once activated, the creations went rogue from their creator, and attacked the population of Cardiff in an event which became known as the All-Night Zombie Horror Show.
The search units took the form of typical zombies. Each "zombie" possessed a residual trace of Rift energy. Like typical zombies, they were unintelligent husks driven by an insatiable hunger and an intrinsic instinct to find the life-shell. They used their bare hands as weapons and cannibalised their victims. They typically had milky white eyes and rotting skin, which was split in places to reveal the sinews and tendons beneath. Some had black gums, drooling a black tar-like drool. To Andy Davidson, the stench of them was like a plague pit or a charnel house. Like their movie counterparts, the only way to kill them was to shoot them in the head.
These "zombies" came in all shapes and sizes: a tall, thin woman with a beehive of black hair and a silk ballgown; a clown, its face a blend of dark rot and white greasepaint; an air hostess, her cap perched on her hairless head; a naked man with a hole in the left side of his face and a Y-shaped post mortem scar stitched with black thread.
The search units were able to use a type of hypnotic suggestion, transferred through their bite, which would turn humans into search units - like a kind of thought-virus. Biologically, the life signs of these humans would remain strong, but they would appear to be zombified. Their face would turn a chalky-white, their breath would turn hot and sour and their lips would curl back from their teeth. They would follow the same instinct as the artificial search units - to find the life-shell and attack anybody in their path. Victims of this thought-virus included Dawn Stratton and Trystan Thomas.
After Leet crashed into the Regal Cinema in Splott, it was disconnected from its life-shell, and took residence inside the body of Oscar Phillips, who thus became the only survivor of the incident. Leet thought the search units into existence from Oscar's memories, the clearest of which were from a screening of zombie movies which he had been watching at the cinema on the night of the crash. The volatility of the memories from which they were created meant that Leet was unable to control its creations. With Cardiff under attack, Leet created a time energy barrier around the city to limit the damage.
The search units stalked the streets of Cardiff. Joe and Jackie Hargreaves were attacked and killed when they ran into one while returning from Llandaff via the A48. A group of students - Toby, Steffan, Curtis, Stan and Greg - were similarly butchered aboard a yacht in Cardiff Bay when a group of the "zombies" climbed out of the sea. Hayley and a further number of students were massacred when the creatures cut-short a house party on Gabalfa Road. Winston -a taxi driver, and Kirsty Lane were cannibalised on Bute Street en route to Oceana. A horde of the units stood guard around St Helen's Hospital, trapping medical staff and patients inside the building.
Control over the search units rested with Oscar, Leet's human host, who had been in a coma since the night Leet lost its life-shell. With the Torchwood Three team under attack, Leet awoke Oscar, who jumped from the window of St Helen's Hospital and renounced control. The search units melted into spirals of glittering light, which rose into the air and disappeared. (PROSE: Bay of the Dead)