Ethel Bossiny is Jane Penvellyn's tutor.
The Penvellyns are protectors of an ancient family secret, passed down from grandparent to grandchild, but the family realized in the sixteenth century that the grandparent may not always be able to reveal the secret to the heir. The Penvellyns befriended the Bossiny family and swore them to secrecy, hiring them as tutors and tasking them with initiating the current Penvellyn heir if the grandparent is unable to.
Five hundred years later, the Bossiny family is still very close to the Penvellyns. Ethel Bossiny tutors the latest heir in the long Penvellyn line, Jane. In addition to teaching her such subjects as French and Mathematics, Ethel initiates Jane to the Penvellyn family secret since her grandfather Alan died when she was very young. When Jane's stepmother Linda becomes bedridden and unusually irritable, a neighbor of Linda's mother named Nancy Drew visits to check up on her. Ethel literally runs into Nancy a few times during her stay, but is always very brief. However, when Nancy appears to be stumbling onto Penvellyn family secrets, Ethel considers her a threat and warns her to back off, since she is uninitiated. If she catches Nancy digging into things she has no business in, Ethel promises to do everything in her power to have her thrown out of Blackmoor Manor, permanently.
- It is unknown whether Ethel was an accomplice in, or even knew about, Jane's plan.