Caleb first encounters the Singularity Generator when it is used on him in the Lafayette Museum of Antiquties by Gideon, the Mad Scientist, and the Prophet guardian. It appears to be an attempt to kill Caleb, but only succeeds in bringing Gabriella through. A subsequent attempt also brings Ishmael through. Caleb picks up the Singularity Generator for his own use in the CabalCo building, and is the last new weapon of the game.
The gun serves as a major plot device, as interdimensional technology is in part responsible for the invasion of Reality Beta and that is involved in the resurrection of the Chosen. Some unused sound files from Blood II: The Chosen REZ file mention a "Channeling Knife" that was severed in two and left somewhere called "Old Town". Gideon mentions that its power is to open up the doors to the realities, so it would probably have been related to the Singularity Generator.
AMMO TYPE: Batteries
REGULAR FIRE: Warms up and fires a large purple vortex which sucks in nearby enemies, causing massive damage
ALTERNATE FIRE: Same as regular