The elements of a prima facie case for professional malpractice are: (1) a breach by the defendant of the duty owed to the plaintiff to conform to a certain standard of conduct; and (2) that the breach of that duty proximately caused an injury or loss to the plaintiff. Id., 1999 ME 196, P10, 742 A.2d 933, 940. the duty owed in this context is the exercise of the "degree of skill, care and diligence exercised by members of that same profession." Fisherman's Wharf Assocs. II v. Verrill & Dana, 645 A.2d 1133, 1136 (Me. 1994). Even if a Plaintiff establishes successfully establishes breach of a duty, proximate cause still must be proved. to prove proximate cause, the claimant must produce an expert witness to testify to the existence of proximate cause. Corey, 1999 ME 196, P14, 742 A.2d at 940. Proximate cause is "that cause which, in natural and continuous sequence, unbroken by an efficient intervening cause, produces the injury, and without which the result would not have occurred." Webb v. Haas, 1999 ME 74, P20, 728 A.2d 1261, 1267. The Law Court has applied this definition to mean that "a negligent act is the proximate cause of an injury only if the actor's conduct is a substantial factor in bringing about the harm." Spickler v. York, 566 A.2d 1385, 1390 (Me. 1989). In Corey, the Plaintiff alleged that the attorney she had hired to represent her in a divorce proceeding committed malpractice by miscalculating the value of her husband's business. the Law Court explicitly stated what she would have to show for her claim to survive summary judgment: Susan must show through expert testimony that the divorce judgment would have been more favorable to Susan if the value of the dental practice had been shown to be higher than the $ 37,700 agreed on... Where the link between the defendant's alleged negligence and plaintiff's alleged loss is overly speculative, summary judgment in favor of the defendant is appropriate. See Steeves v. Bernstein, Shur, Sawyer & Nelson, P.C., 1998 ME 210, P13, 718 A.2d 186, 190. In Corey, the plaintiff's statement of material facts did not state that the expert would testify as to the fact that she would have been successful in causing the trial court to accept the higher value of her husband's business, or that part of it would have been awarded to the plaintiff. See 1999 ME 196, P14, 742 A.2d at 940. That lack of expert evidence regarding a different outcome based on the defendants' negligence rendered the Plaintiff's claims speculative. Id.