Martha was last seen in Bridgewater, Virginia at approximately 12:00 p.m. on August 3, 1973. She was accompanied by her sister, Flora, and Flora's employer, John Keyton, at the time. They were driving Keyton's light green 1967 Ford Fairline to a family reunion at the home of Keyton's brother in Dabolt, Kentucky; the event was scheduled for the following day. Keyton and Helmicks never arrived and have never been heard from again.

Keyton was not a good driver in 1973. He had been in at least one accident and received many traffic citations. His driver's license had been taken from him, but he continued to drive. Some theorize that he and the Helmick sisters died in an vehicular accident in the mountains of Virginia or Kentucky. If so, their remains and their car were never found.

A search turned up no sign of the Helmicks or Keyton. Martha usually sent postcards to her loved ones when she traveled, but none of them heard from her after her disappearance. Their cases remain unsolved.