Terrible trickster: sword girl book 5, the

A trickster is turning life at Flamant Castle upside down. Someone has put sneezing powder in the knights' soup and itching powder in Sir Walter's sheets and changed the salt for sugar in Mrs Moon's kitchen. At first the tricks seem funny, but Sir Benedict is not amused. He thinks the trickster is Tommy - and unless the tricks stop, he will send her away from the castle! Can she find out who the real trickster is before she is banished forever?