The basic concept of occultus is the question 'what if?' How would the removal of one character affect the lives of the rest of the characters we know and love?

In this world, Tom Riddle never existed. There was no Voldemort. No Death Eaters. And no Order of the Phoenix.

However, just because Voldemort didn't exist doesn't mean that the prejudice against Muggleborns is gone. A group made up of members from some of the old Pureblood families (ie: the ones who would be known as Death Eaters in the books) is currently in power at the Ministry, instilling fear of the Muggles and Muggleborns within society. This group are known as The Knights of Walpurgis and their current agenda is to remove the "Muggleborn Threat" from the wizarding world. But, the Knights know that killing people is generally frowned up in society so they came up with a plan to take over the Ministry and subtly nudge the Muggleborns "out the door", so to speak.

The Ministry in occultus is run very similar to how it was run in Harry Potter and the Deathly Hallows, where Muggleborns are forced to register like any other beast/being. Those who don't register are placed into Azkaban for six to twelve months (or until the Muggleborn cracks and registers). Any further refusal to register can have the Muggleborns wand snapped and them thrown out of the wizarding world.

Muggleborns that do register generally have no problem and can continue to live quite normal live in the wizarding world. However, due to the prejudice the Ministry has created against them, Muggleborns are not welcomed everywhere.

Muggleborns will find it very difficult to get a job in the Ministry because the Knights know that to keep power the public must remain blind to the prejudice against them. However, Muggleborns are generally free to get jobs in other industries (eg: St. Mungo's) they just won't hold high positions within them.

Most of the general public are unaware the prejudice even exists and think everything is all good with the world. But there is a group working with the Muggleborns to over throw the Knights and current Ministry and build a fairer society for all... this group, of course, is the Order of the Phoenix.

The game starts on 31st October, 1998 (31st Oct, 2011 - real time) with a Halloween Festival being held by the Ministry as a Charity Event to support the new Children's Ward at St. Mungo's Hospital. The event will be filled with Pureblood Supremacists and a group of vigilantes will use the event to try and assassinate the Minister - Pius Thicknesse.

The Order will be blamed despite having nothing to do with the assassination attempt. Giving the Knights the upper hand in public opinions and causing the Order to be branded as outlaws. Because of this, if a person is known to be a member, they are thrown into Azkaban for treason (an offense that carries a maximum sentence of 10 years). Hence the Order now have to work in secrecy if they want to take over the wizarding world and make it a better place.