Sandra "Sandy" Alvarez was born and raised in a rough neighborhood in East Los Angeles. The youngest of 5, and the only girl amongst them, she grew up to be a bona fide tomboy. Losing her parents at a young age, Sandy and her brothers were raised by their abuela, who made her living conducting seances for others in their neighborhood, as well as doing tarot readings and offering other services as the local "curandera" (healer/witch doctor).

As a way of getting out of el barrio she grew up in, she pursued a career with the US National Park Service. She worked as a park ranger in Yosemite for a few years, until one unfortunate day that almost cost Sandy her life. Barely surviving a bear attack, Sandra Alvarez fell prey to a landslide caused by an earthquake in the area. Finding herself dead underneath the rubble that crushed her, she was approached by a primal and gruesome entity that offered her a chance to live again as long as it could tag along for the ride. Begrudgingly, she accepted the deal, and thus sealed her fate through the bargain made with her Geist, who she refers to as "El Cucuy," a reference to the boogeyman of the stories she was told by her abuela when she was young.

With a newfound purpose, Sandra considers herself a Gatekeeper, working hard to ensure that the barriers between the living and dead remain in place. She recently relocated to New York City, which is very different from what she's used to. She sort of hates the place, not feeling at home in such a big city after the years she spent as a park ranger. However, two of her brothers share an apartment in the city, which is what has brought her to NYC. With abuela and "Puchi" (her oldest brother) having passed on, and Diego serving a lifetime sentence at USP Atwater for his involvement in several crimes tied to his gangster lifestyle, Santiago and Lucho are the only two family she's got left in the US.