Tomasina Morgenstern, most often called "Missy", is the delicate and sheltered daughter of a powerful industrial tycoon. She is betrothed to explorer and socialite Arthur Swiftwood, and wil thereby become Lady Swiftwood of Oaksleigh. She dotes upon her love with abandon and seems thrilled to move into Swiftwood Manor and begin her life with him.

Beauty may not be everything, but the young and beautiful Tomasina Morgenstern has beauty in excess. Tall, thin, and blonde, Tomasina is the youngest child and only daughter of steel and oil magnate Theodore Morgenstern and as such was reared to be soft-spoken, well-mannered, and obedient. When Tomasina attended the funeral of one of her father's business associates she met the eldest son of the deceased, Lord of Oaksleigh Arthur Swiftwind, who had recently returned from just over two decades of adventuring. Captivated and emboldened by her sudden and inexplicable attraction to this man, Tomasina insisted that her elder brother chaperone her and Arthur the following Monday for a teatime meeting. Arthur quickly turned out to be just as taken with Tomasina as she was with him, and soon the couple was courting in the open. Before either of them knew it, Tomasina and Arthur were betrothed and Arthur stood to gain a great deal through his soon-to-be familial relationship with Tomasina's father, Theodore. Theodore approved of Arthur as his daughter's choice of spouse but began scrutinizing the younger man much more intensely as soon as the engagement was official. To the surprise (and in some cases, disdain) of Bellaerie high society, Tomasina moved into Arthur's family home shortly after their betrothal was announced, and has lifted some of the grief around Lannora Ivy with her characteristic cheer.