Secrets of the Silent Witch, Vol. 5 (manga)

When Monica is invited by Caroline, the girl who caused her to fall down the stairs, to a tea party, she has her doubts but can't find it in her to refuse. Sure enough, Caroline reveals her true motives at the tea party, demanding that Monica tell Cyril that the incident the other day was an accident! Monica stands firm, but when she drinks the tea Caroline offers her, she starts to feel something strange...

and the person who rushes to her rescue is none other than--Claudia?!