Venetian Mask; by Rosalind Laker.

"Two friends who were resident pupils in a convent in Venice and had more spirit than could be tamed by the convent begin in this story by going to the festivities using masks, which everyone does of course, so they are not detected, and thus begins this story, a story of friendship of the two for life, while they find love and marriage - not necessarily always found together - and challenges in life that they face with courage and always manage to overcome with help of each other. Sounds glib, but the story is quite serious, and one gets very close to the characters, especially the two women, going through their travails with them as one reads this."