Isidro Issued a Negotiable Promissory Note to His Attorney in Return

Isidro issued a negotiable promissory note to his attorney in return for the attorney's promise to perform legal services. The attorney never rendered the legal services but quickly negotiated the note to Anna, a holder in due course. Anna and Mark were involved in business negotiations and Anna offered to purchase a car from Mark. She offered as part payment for the car the note issued by Isidro. By coincidence, Mark knew both Isidro and the attorney and the facts concerning the note and the unperformed legal services. Despite this, Mark accepted a negotiation of the note from Anna. Isidro refused to pay the note and Mark eventually sued Isidro to collect. What is the probable outcome?