(art from Sunless Sea)

The Lady in Black is a mysterious character that may be tied to death itself. What she actually is has currently not been revealed.

(WARNING: major spoilers for Sunless Sea.)

The Lady In Black
The brave zailor who performs the Abyssal Rites properly will meet her face-to-face. None have done this and lived. Choose life, or choose death...
The folds of her dress drape about you. They are snug and familiar as your bedsheets. Sleep takes you.

You awake. You are home in your lodgings. There is the crack in the ceiling you know so well, and the chip on the bedpost. The covers float lazily off you. The darkness is abyssal, but your candles glow with St Brendan's fire. You swim to your window. London's streets are empty, and not as you remember them. Your favourite haunts are joined in a row, all within convenient walking distance. Silent, deserted; reserved only for you. Beyond them are houses centuries older, all abandoned. A playful current tugs at you. A familiar voice. You open your window, and allow the current to carry you to Lady Black's colonnaded palace. Perhaps today, her Ladyship will desire conversation, or a swim through her glowing gardens. Perhaps (you shudder) she has decided to resume the violin. Or perhaps she merely wants to sit at her watery hearth in companionable silence. What would she do without you?

The coffin speeds upwards. Lady Black follows you, silently. She does not labour to keep pace. She examines you through your face-visor with fierce interest, as though trying to commit your every feature to memory.

After seven minutes she sighs.

After fourteen minutes she plucks a strand of her coiling hair, and ties it to your line.

After twenty one minutes, as your zubmarine comes into view, she grasps your hand. She squeezes your fingers urgently. Then her hand slips from yours, and she is gone.