Conspiracy was released on 21 August 1989 through Roadrunner Records, and is the last album to feature drummer Mikkey Dee who left the group but recorded the album as a session member.

The song "Cremation" appears in the 2009 video game Brütal Legend.

He makes a deal with "Them", the unseen demonic antagonists from the previous album, to return control of the house to "Them" in exchange for the chance to see his now-dead sister Missy again, as he believes she can help answer some of his questions ("Sleepless Nights").

He attends sessions with a therapist named Dr. Landau, who he despises, distrusts and lies to; Landau suggests letting King's mother visit the House of Amon, and King reluctantly agrees ("Lies").

All tracks are written by King Diamond, except where indicated"The Wedding Dream" contains the elements of "Bridal Chorus" by Richard Wagner in the introduction.