Summer disappeared with her husband of three years, Joseph, and their two sons, Joseph Jr. and Gianni. The family was last seen in Fallbrook, California on February 4, 2010. A surveillance camera from a neighbor's home security system shows a car pulling out of the driveway at 7:47 p.m. The last contact was when Joseph called a business associate at 8:28 p.m. None of them were ever heard from from again.

Four days after they were last seen, authorities located the family's white 1996 Isuzu Trooper parked illegally at a strip mall in San Ysidro, California, eighty miles from home and just a few blocks from the Mexican border. The children's car seats were still inside it. The car was towed and put in an abandoned vehicle lot. The McStays weren't reported missing until February 15, when Joseph's brother asked police to do a welfare check on their home because he hadn't been able to get in touch with them.

Summer is a licensed real estate agent and worked for a real estate business at the time of her disappearance, and Joseph owns Earth Inspired Products, an Internet-based business that designs decorative water fountains and ships internationally. His brother stated he would not abandoned his company and left without warning. Authorities stated that although they found no hard evidence of foul play, nothing at the McStays' residence indicated they planned to be gone for an extended period and they were treating the disappearances as suspicious. The family's dogs had been left outside without food and there were recently purchased groceries in the kitchen, including some items left out that should have been refrigerated. They had recently moved to Fallbrook from Laguna Nigel, California. Joseph and Summer had a good marriage. Investigators could uncover no evidence of personal problems within the family, financial problems or criminal activity, although Joseph's business partner had served time in prison for theft-related offenses.

Because their car was found so close to the border, authorities looked into the possibility that the family went to Mexico. They discovered a surveillance video from a border-area business that shows a man, a woman and two children walking towards Mexico at the San Ysidro point of entry at 7:00 p.m. on February 8, the same day the McStays' car was found. The people resembled the McStays, but their family members who viewed the film unable to identify them because the image quality was poor. Joseph may have occasionally gone to Mexico for business, but he never took his family with him. One of Summer's friends stated the two of them had discussed the idea of vacationing in Mexico and Summer said she thought it was too dangerous to travel there. Joseph had a valid passport, but Summer's passport was expired and the children had never had passports. However, computer records show that shortly before they disappeared, the McStays had looked up the passport rules for children traveling to Mexico.

Since their disappearances, Joseph and Summer haven't used their bank accounts, cellular phones or credit cards. Authorities believe they went to Mexico intentionally, but it's unclear what happened to them after that, and their family fears they may be in danger and may have met with foul play. Their cases remain unsolved.