James Courville, John Grisham and Rob Wilburn co-owned Trinity Clinical Laboratory, and in 2019 all three were named in a federal healthcare-fraud investigation; Courville retained Katten Muchin Rosenman LLP and its lawyers Barrett Howell and Ryan Meyer, while Grisham and Wilburn were represented by separate counsel.¹ The pleading alleges the parties and their counsel entered into an oral joint defense agreement, reaffirmed in July 2020, that protected shared confidences, and that the Katten lawyers meanwhile had Courville proffer to the government and become a confidential human source.² Grisham and Wilburn were indicted in September 2021 and Courville was not, they say they learned only in January 2024 that Courville had worked for the government, and the charges against them were later dismissed with prejudice.³ They allege the Katten lawyers lied, supported Courville's grand-jury perjury and shared information learned under the agreement with the prosecutor, while the lawyers say they only defended their own client and that Courville acted as an informant against a different person.⁴

Grisham and Wilburn sued the Katten lawyers and the firm, the lawyers moved to dismiss under Rule 91a on the basis of attorney immunity, and on August 27, 2025 the 160th District Court of Dallas County denied the amended motion without explanation.¹ The Fifth Court of Appeals (Dallas) denied mandamus on January 22, 2026, agreeing that the conduct "falls within the scope of legal representation" but finding a question whether the parties were adversarial for immunity purposes.² The lawyers petitioned this Court, which requested a response in March 2026, and set the case for oral argument on September 4, 2026, ordering merits briefing.

Original proceeding for writ of mandamus from the Fifth Court of Appeals' denial of mandamus on a Rule 91a ruling; argument set September 4, 2026. Oral argument: February 10, 2027.

• The Katten lawyers:¹ (1) whether it was a clear abuse of discretion to deny the Rule 91a motion where all the conduct alleged relates to representing a separate client in a criminal case; and (2) whether they lack an adequate remedy by conventional appeal.
• Grisham and Wilburn:² whether attorney immunity applies to these facts, including whether the relationship was sufficiently adversarial under Haynes & Boone v. NFTD, whether the Barcelo factors are present and whether violations of penal statutes defeat immunity, and whether a lawyer who enters a joint defense agreement owes each party a fiduciary duty.

A Rule 91a claim has no basis in law if the allegations, taken as true, do not entitle the claimant to relief or affirmatively negate entitlement, and mandamus requires a clear abuse of discretion and no adequate appellate remedy.¹

Whether attorney immunity bars the claims.

The Katten lawyers (Relators): Attorneys are immune from civil liability to non-clients for actions taken in representing a client, the conduct alleged was all part of representing Courville in a criminal investigation, and co-subjects of an investigation are inherently adverse because each wants to protect himself, so the adversity requirement is met on the face of the pleading.¹ In reply, the lawyers say a joint defense agreement is simply a contract and a tool for sharing information between lawyers whose clients have separate interests, that it does not remove adversity, and that other remedies such as disqualification exist.²

Grisham and Wilburn (Real Parties in Interest): The attorney-immunity doctrine does not apply because by joining the agreement the Katten lawyers' client became aligned with the plaintiffs and the lawyers were not opposing counsel, none of the Barcelo factors justifying immunity is present, and immunity does not cover violations of a penal statute.³

Whether each cause of action falls within the lawyers' role.

The Katten lawyers (Relators): Each of the plaintiffs' claims, including fraud, negligent misrepresentation, breach of fiduciary duty, DTPA violations, breach of contract, negligence, aiding and abetting and negligent hiring and supervision, complains of conduct within the role and duties of a lawyer.⁴

Grisham and Wilburn (Real Parties in Interest): A lawyer who enters a joint defense agreement owes each party a fiduciary duty to preserve confidences as if they were clients, as Godbey and Armco recognized, and letting immunity defeat that duty would leave co-targets with no remedy and make such agreements worthless.⁵

Whether mandamus is available.

The Katten lawyers (Relators): Mandamus is appropriate when a trial court wrongly denies a Rule 91a motion, and the right to immunity would be effectively lost if they must wait for an appeal.⁶

The lawyers argued that the case presents a fundamental question for the adversarial system, whether attorney immunity protects a lawyer who successfully represented a client in a criminal case from civil claims by non-clients about that representation, and that the lower courts' rulings produce the exposure to "loyal, faithful, and aggressive representation" liability the doctrine exists to prevent.¹ Grisham and Wilburn responded that this case is not the occasion to rewrite rules that have stood for three decades.²

None noted