Sips initially started recording Orcs Must Die! videos on 17th December 2011, being the second series of videos that he ever created (with the first being Dig-N-Rig). The series quickly grew into one of Sips' (if not the) most successful game playthroughs to-date. The series came to a close on 12th March 2012.
Sips is currently playing Orcs Must Die 2.
Sips' series wasn't the first time that Orcs Must Die! had been recorded by the Yogscast. The game actually first featured in the Battlefield 3 LAN videos, as Simon and Lewis had spent much of their time playing Orcs Must Die! and Minecraft.
The story revolves around the Order, an elite faction of wizards and warriors who guard the Rifts, magical openings between the human world and the 'Dead World', which provide a source of magical power throughout both worlds. Using this power, the Order is able to maintain a perfect world for humanity by using magic to manipulate nature. In order to protect the human world, they have constructed magically-empowered fortresses throughout the Dead World to guard the Rifts, particularly from the adversarial faction known as 'the Mob' - a brutish horde of creatures such as Orcs, Ogres and Gnolls which, despite being unintelligent, still pose a major threat to the human world due to their vast numbers.
After a surprise attack by the Mob, the player character, known only as 'the Apprentice', finds himself as the last living member of the Order, as the Mob appears to have suddenly obtained a surge in both strength and intelligence. Taking it upon himself to defend the human world, he defends the fortresses from the Mob one by one (much to the bewilderment of his teacher, who narrates the storyline). The Apprentice eventually learns that the Mob has been empowered by the Sorceress, a past student of the Order who, despite showing overwhelming potential to help defend humanity, instead chose to seek power for herself and used magic to seize control of the Mob. The player receives help from Guardians, and although most people aren't on a first name basis with these Guardians, Sips is, and calls them by their names (Steves, Sons of Winston, etc).
As the Mob's attacks become more and more aggressive, the Apprentice eventually chooses to ensure the safety of the human world by stepping back through a Rift and closing them all forever by means of a simple spell. Although this means that the Mob can never reach the human world, it also means that humanity is no longer able to use magic to sustain itself, and the whole world, which has become dependent on magic, begins to deteriorate. In the Dead World, the Sorceress is rendered powerless as the Rifts can no longer provide her with magic, and she is left at the mercy of the Mob, who have been reduced to their original state.