(1) Where, in the case of an action for which a period of limitation is fixed by this Act, either -

(a) the action is based on the fraud of the defendant or his agent or of any person through whom he claims or his agent, or

(b) the right of action is concealed by the fraud of any such person,

the period of limitation shall not begin to run until the plaintiff has discovered the fraud or could with reasonable diligence have discovered it.

(2) Nothing in subsection (1) of this section shall enable an action to be brought to recover, or enforce any charge against, or set aside any transaction affecting, any property which has been purchased for valuable consideration by a person who was not a party to the fraud and did not at the time of the purchase know or have reason to believe that any fraud had been committed.