Saul had been Mark corporate lawyer for more than a decade. Mark 's daughter, Sylvia, who is in first year law, hopes to join Saul's law firm upon graduation.

Mark owes Saul $50,000 for professional services. Saul suggests to Mark that the account could be settled if Mark were to transfer his condo to Saul. The $50,000 debt would represent Saul's down payment and Mark would carry the balance of the price, $200,000, by way of a vendor take-back mortgage.

At first, Mark hesitated, but reflecting upon his need for Saul's legal expertise and his daughter's career, he agreed.

A few months later, Mark's son David, who was to inherit the condo, learned of the transaction and persuaded his father to sue to recover his inheritance.

a. What is the most likely cause of action that could be used by Mark to recover the condo? What would Mark need to prove to be successful?

b. What possible arguments could Saul use in defense