The remainder of this cover page shall be filled out for a reporting person’s initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter disclosures provided in a prior cover page.

  Names of Reporting Persons.

  Alta Fundamental Advisers LLC

  Check the Appropriate Box if a Member of a Group (See Instructions)

  (a)  ☐        (b)  ☐

  SEC Use Only

  Source of Funds (See Instructions)

  OO

  Check if Disclosure of Legal Proceedings Is Required Pursuant to Items 2(d) or 2(e)

  ☐

  Citizenship or Place of Organization

  Delaware

Number of

Shares

 Beneficially 

Owned by

Each

Reporting

Person

With

  Sole Voting Power

  1,947,093

  Shared Voting Power

  0

  Sole Dispositive Power

  1,947,093

  Shared Dispositive Power

  0

  Aggregate Amount Beneficially Owned by Each Reporting Person

  1,947,093

  Check if the Aggregate Amount in Row (11) Excludes Certain Shares (See Instructions)

  ☐

  Percent of Class Represented by Amount in Row (11)

  14.8%

  Type of Reporting Person (See Instructions)

  IA

Item 1.

Security and Issuer

This Schedule 13D relates to the ordinary shares, par value $0.01 per share (“Ordinary Shares”), of Mallinckrodt plc (the “Issuer”), which has its principal executive offices at College Business & Technology Park, Cruiserath, Blanchardstown, Dublin 15, Ireland.

Item 2.

Identity and Background

(a)   This Schedule 13D is being filed by Alta Fundamental Advisers LLC (“Alta Advisers” or the “Reporting Person”).

(b)   The address of the principal business office of the Reporting Person is 1500 Broadway Suite 704, New York, NY 10036.

(c)   The principal business of the Reporting Person is acting as an investment adviser to private funds and managed accounts.

(d)   During the last five years, neither the Reporting Person, nor to the Reporting Person’s knowledge, any of the persons listed in Schedule A, has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors).

(e)   During the last five years, neither the Reporting Person, nor to the Reporting Person’s knowledge, any of the persons listed in Schedule A, has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceeding was or is subject to a judgment, decree of final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

(f)   The Reporting Person is a Delaware limited liability company.

Schedule A attached hereto sets forth the information regarding the manging members of the Reporting Person.

Item 3.

Source and Amount of Funds or Other Consideration

The funds used in purchasing shares of Ordinary Shares on behalf of clients of Alta Advisers come from private funds and various client accounts advised by Alta Advisers.

Item 4.

Purpose of Transaction

On June 16, 2023, the Reporting Person sent a letter to the Issuer’s board of directors (the “Board”) with respect to the requisition of the Board to convene an extraordinary general meeting of the Issuer’s shareholders. A copy of the letter is attached to this Schedule 13D as Exhibit 1 and is incorporated by reference herein.

The Reporting Person expects to continuously review its investment in the Issuer and, depending on various factors including but not limited to, the price of the shares of the Ordinary Shares, the terms and conditions of the transaction, prevailing market conditions and such other considerations as such Reporting Person deems relevant, may at any time or from time to time, and subject to any required regulatory approvals, acquire or dispose of additional Ordinary Shares from time to time on the open market, in privately- negotiated transactions, directly from the Issuer, or pursuant to other transactions.

Item 5.

Interest in Securities of the Issuer

(a)   The information set forth in rows 11 and 13 of the cover page to this Schedule 13D is incorporated by reference. The percentage set forth in row 13 is based on 13,170,932 Ordinary Shares outstanding as of May 5, 2023, as reported in the Issuer’s Form 10-Q filed on May 9, 2023. Managed funds and clients advised by Alta Advisers directly hold 1,947,093 Ordinary Shares.

(b)   The information set forth in rows 7 through 10 of the cover pages to this Schedule 13D is incorporated by reference.

(c)   Schedule B sets forth all transactions with respect to the Ordinary Shares effected during the past sixty days by the Reporting Person.

(d)   The funds and clients advised by Alta Advisers have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Ordinary Shares.

(e)   Not applicable.

Item 6.

Contracts, Arrangements, Understandings or Relationships with Respect to Securities of the Issuer

The information set forth in Item 4 above is incorporated by reference into this Item 6.

Affiliates of the Reporting Person hold first lien debt and first lien bonds of the Issuer.

Item 7.

Material to be Filed as Exhibits

Exhibt 1 Letter to the Board of Directors of Mallinckrodt plc, dated June 16, 2023.

Alta Advisers

Name and

Citizenship

Position

Principal Business Address

Beneficial Ownership of
Ordinary Shares

1500 Broadway Suite 704

New York, NY 10036

1500 Broady Suite 704

New York, NY 10036

Managed Fund or Account

Managed Fund or Account

Managed Fund or Account