Dale copes with the fallout from Maddie and Ryn's encounter with the man from Susan's past; Katrina tries to get the rest of the pack to join her side.
Tensions rises following a shocking discovery; The water tank starts to have an adverse effect on the mermaids; Ryn makes a deal with a complicated ally.
An unsuccessful mating season leads to questioning the possibility of the mermaids procreating on land; Ryn brings a new mate for the good of the colony.
Ben and Xander deal with a shocking discovery about Chris and his connection to the military; Helen and Maddie reluctantly seek help from the hybrids as the threat of extinction looms.