Onyx and Sea is a stand alone book that takes place after The Edge Of The World arc.
Happy with her new life in RiverClan, Seabreeze starts to feel at home, especially with Onyxsplashed who she loves dearly.
One day while on a border patrol, they discover a lone wandering loner whom they take back to the clan as she had no memory of who she was aside from her name, taking her to the medicine cat for help. A few days later they speak with Northstar, who later names her, Nymphpaw and assigns Onyxsplashed and Seabreeze as her mentors.