Abigail is found at the Sonar Collections Dock when playing as Michael De Santa after purchasing the dock. Abigail speaks about her husband Frank Mathers and his death in a submarine accident. The insurance company believes that the submarine was tampered with and is unwilling to pay Abigail. She asks Michael if he would find the missing Submarine Parts in order to prove to the insurance company that there was no foul play. Abigail gives Michael a Dinghy with sonar in order to find the missing Submarine Parts. The parts can be found by any character after the mission has been started by Michael. Once the player finds all 30 submarine parts, the mission What Lies Beneath automatically begins.
Talk with Abigail
Find all 30 Submarine Parts
After the mission is unlocked, news reports regarding Mathers' disappearance are heard on Weazel News and available online.
For unknown reasons, if the dock is purchased after the events of Minor Turbulence, this event won't appear, becoming unplayable for the rest of the game. To avoid this, the player must buy the dock and play the event before that particular mission. Note that this seems to be patched on the PC version, as Abigail will show up as a blue question mark after purchase, no matter when.