Dr. Maya Calder, a marine biologist in Havenport, Maine, discovers an unsettling phenomenon: crabs are dying without visible cause. Initially dismissed by local officials focused on tourism, Maya's concerns escalate as more marine life exhibits similar symptoms. She teams up with Ben Carrick, an old fisherman whose generational knowledge of the sea aligns with her scientific observations of the unusual scarcity of sand eels and lethargic lobsters.
After a flounder dies with signs of suffocation despite normal oxygen levels, Maya sends samples to her former mentor, Dr. Aris Thorne. Thorne identifies a highly potent, undetectable Cold War neurotoxin codenamed "Silent Tide," designed to mimic natural causes of death. He reveals it's an old leak, not a new one, prompting Maya to suspect a sunken military vessel in the treacherous "Graveyard" channel.
