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Exhibit 4.2(n)    
  

        February 13,
2002 

The
Bank of New York,

as trustee under the Guarantee Agreement referred to below

101 Barclay Street, 21 West

New York, New York 10286

Attention: Vice President, Corporate Trust Administration 

Re:
The Montana Power, L.L.C./Assumption of Guarantee 

Ladies
and Gentlemen: 

        Reference
is made to the proposed merger (the "Merger") of The Montana Power Company, a Montana corporation
("MPC"), with and into The Montana Power, L.L.C., a Montana limited liability company ("MPC LLC"), which
Merger is expected to be completed on or about the date hereof. Reference is further made to the Guarantee Agreement, dated as of November 1, 1996, between MPC and The Bank of New York as
trustee. 

        Effective
upon consummation of the Merger, MPC LLC hereby assumes and agrees to be bound by all of the guarantees, covenants and agreements on the part of MPC to be performed or observed
under the Guarantee Agreement as successor to MPC under such agreement. 

	 	 	THE MONTANA POWER, L.L.C.
	

 	
 	
By:	

/s/  PATRICK T. FLEMING      
 Name: Patrick T. Fleming

Title: V.P., General Counsel & Secretary

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Exhibit 4.2(n)QuickLinks
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Exhibit 4.2(o)    
  

Execution Version  

  
 

    ASSUMPTION AGREEMENT
  (QUIPs GUARANTEE)    
  

        This Assumption Agreement (QUIPs Guarantee) (this "Assumption
Agreement") is made and entered into as of November 15, 2002 between Northwestern Energy, L.L.C., a Montana limited liability company
("Assignor", formerly known as The Montana Power, L.L.C., successor by merger to The Montana Power Company
("MPC")), and NorthWestern Corporation, a Delaware corporation ("Assignee"). 

        WHEREAS,
Assignor is a party to that certain Indenture, dated as of November 1, 1996 (the "Indenture"), between Assignor and The
Bank of New York, as trustee (the "Trustee") under which were issued Assignor's Quarterly Income Preferred Securities (the
"QUIPs"); 

        WHEREAS,
Assignor is also party to that certain Guarantee, dated November 1, 1996, by and between MPC and the Trustee (the
"Guarantee"), pursuant to which Assignor guaranteed the QUIPs; 

        WHEREAS,
pursuant to the Asset and Stock Transfer Agreement, dated as of November 15, 2002, between Assignor and Assignee, the parties propose to consummate a restructuring
transaction involving the assignment by Assignor to Assignee and the assumption by Assignee of substantially all of Assignor's assets and liabilities (the
"Transaction"); and 

        WHEREAS,
in connection with the Transaction, Assignor and Assignee are entering into this Assumption Agreement to specifically transfer and assign to Assignee, and for Assignee to
assume, all of Assignor's obligations under the Guarantee; 

        NOW,
THEREFORE, for and in consideration of the premises and the mutual covenants contained herein, and for other good and valuable consideration, the receipt, adequacy and legal
sufficiency of which are hereby acknowledged, the parties do hereby agree as follows: 

	1.
	All
capitalized terms set forth herein and not otherwise defined herein are used herein as defined in the Guarantee.

	2.
	Assignor
hereby assigns, transfers and conveys and sets over to Assignee, its successors and assigns, from and after the date hereof (collectively, the
"Assignment") all of Assignor's obligations and liabilities under and in connection with the Guarantee.

	3.
	Assignee
hereby accepts the Assignment and assumes and agrees, from and after the date hereof to pay, perform and discharge when due all of Assignor's obligations and liabilities
under, and to assume the due and punctual performance and observances of each term, covenant, condition and promise in Guarantee, to be performed and observed by Assignor, as fully and completely as
though it were originally named therein.

	4.
	This
Assumption Agreement shall be governed by and construed in accordance with the laws of the State of New York, determined without reference to principles of conflicts of laws. 

[Signature
Page to Follow] 

        IN
WITNESS WHEREOF, the parties have executed this Assumption Agreement as of the date first written above. 

	 	 	ASSIGNOR:

 NORTHWESTERN ENERGY, L.L.C.
	

 	
 	
By:	

/s/  MICHAEL K. HANSON      
 Name: Michael K. Hanson

Title: President and CEO

	 	 	ASSIGNOR:

 NORTHWESTERN CORPORATION
	

 	
 	
By:	

/s/  ERIC R. JACOBSEN      
 Name: Eric R. Jacobsen

Title: SVP, General Counsel and CLO

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Exhibit 4.2(o)

ASSUMPTION AGREEMENT (QUIPs GUARANTEE)QuickLinks
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Exhibit 4.2(q)    
  

Execution Version  

  
 

    ASSIGNMENT AND ASSUMPTION AGREEMENT
  (QUIPs AGREEMENTS)    
  

        This Assignment and Assumption Agreement (QUIPs Agreements) (this "Assignment and
Assumption Agreement") is made and entered into as of November 15, 2002 between Northwestern Energy, L.L.C., a Montana limited liability company
("Assignor", formerly known as The Montana Power, L.L.C., successor by merger to The Montana Power Company
("MPC")), and NorthWestern Corporation, a Delaware corporation ("Assignee"). 

        WHEREAS,
Assignor is a party to that certain Indenture, dated as of November 1, 1996 (the "Indenture"), between Assignor and The
Bank of New York, as trustee (the "Trustee") under which were issued Assignor's Quarterly Income Preferred Securities (the
"QUIPs"); 

        WHEREAS,
Assignor is also party to that certain Agreement as to Expenses and Liabilities, dated November 1, 1996, by and between MPC and Montana Power Capital I, (the
"Expense and Liability Agreement"); 

        WHEREAS,
Assignor has certain obligations in connection with the Amended and Restated Trust Agreement of Montana Power Capital I, dated as of November 1, 1996, among MPC, as
Depositor, the Trustee, as Property Trustee, The Bank of New York (Delaware), as Delaware Trustee and Ellen M. Senechal, Jerrold P. Pederson and Pamela K. Merrell, as Administrative Trustees (the
"Trust Agreement") relating to the "Obligations" (as defined therein); 

        WHEREAS,
pursuant to the Asset and Stock Transfer Agreement, dated as of November 15, 2002, between Assignor and Assignee, the parties propose to consummate a restructuring
transaction involving the assignment by Assignor to Assignee and the assumption by Assignee of substantially all of Assignor's assets and liabilities (the
"Transaction"); and 

        WHEREAS,
in connection with the Transaction, Assignor and Assignee are entering into this Assignment and Assumption Agreement to specifically transfer and assign to Assignee, and for
Assignee to assume, all of Assignor's rights and obligations under the Expense and Liability Agreement and in connection with the payment of the "Obligations" as set forth in the Trust Agreement; 

        NOW,
THEREFORE, for and in consideration of the premises and the mutual covenants contained herein, and for other good and valuable consideration, the receipt, adequacy and legal
sufficiency of which are hereby acknowledged, the parties do hereby agree as follows: 

	1.
	All
capitalized terms set forth herein and not otherwise defined herein are used herein as defined in the Trust Agreement and the Expense and Liability Agreement, as applicable.

	2.
	Assignor
hereby assigns, transfers and conveys and sets over to Assignee, its successors and assigns, from and after the date hereof (collectively, the
"Assignment") all of Assignor's rights, interests, title, benefits and privileges in and to, and all of Assignor's obligations and liabilities in
connection with each of the following Agreements (collectively, the "Assigned Agreements"):

	(a)
	the
Trust Agreement; and

	(b)
	the
Expense and Liability Agreement. 

	3.
	Assignee
hereby accepts the Assignment and assumes and agrees, from and after the date hereof to pay, perform and discharge when due all of Assignor's obligations and liabilities
under, and to assume the due and punctual performance and observances of each term, covenant, condition and promise in the Assigned Agreements, to be performed and observed by Assignor, as fully and
completely as though it were originally named therein.

	4.
	This
Assignment and Assumption Agreement shall be governed by and construed in accordance with the laws of the State of New York, determined without reference to principles of
conflicts of laws. 

        [Signature
Page to Follow] 

        IN
WITNESS WHEREOF, the parties have executed this Assignment and Assumption Agreement as of the date first written above. 

	 	 	ASSIGNOR:

 NORTHWESTERN ENERGY, L.L.C.
	

 	
 	
By:	

/s/  MICHAEL K. HANSON      
 Name: Michael K. Hanson

Title: President and CEO

	 	 	ASSIGNEE:

 NORTHWESTERN CORPORATION
	

 	
 	
By:	

/s/  ERIC R. JACOBSEN      
 Name: Eric R. Jacobsen

Title: SVP, General Counsel and CLO

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Exhibit 4.2(q)

ASSIGNMENT AND ASSUMPTION AGREEMENT (QUIPs AGREEMENTS)QuickLinks
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Exhibit 4.2(y)    
  

 
 

THE MONTANA POWER, L.L.C.
  
  TO
  
  THE BANK OF NEW YORK
  
  Trustee    
  

 
 

FIRST SUPPLEMENTAL INDENTURE
  (For Unsecured Subordinated Debt Securities
  relating to Trust Securities)
      
  

Dated as of February 13, 2002  

        FIRST SUPPLEMENTAL INDENTURE, dated as of February 13, 2002, between THE MONTANA POWER,
L.L.C., a limited liability company duly organized and existing under the laws of the State of Montana (herein called "MPC
LLC"), having its principal office at 40 East Broadway, Butte, Montana 59701, THE BANK OF NEW YORK, a corporation duly organized
and existing as a banking corporation under the laws of the State of New York, having its principal corporate trust office at 101 Barclay Street, New York, New York 10286, as Trustee (herein called
the "Trustee"), supplementing the Indenture, dated November 1, 1996, between The Montana Power Company, a corporation organized under the laws of
the State of Montana ("MPC"), and the Trustee (the "Indenture"). 

 
 

RECITALS    
  

        WHEREAS,
MPC has entered into an Agreement and Plan of Merger among MPC, Touch America Holdings, Inc. (a Delaware corporation and a wholly-owned subsidiary of MPC), and MPC LLC (a
wholly-owned subsidiary of Touch America Holdings, Inc.), dated as of February 20, 2001, pursuant to which MPC has merged with and into MPC LLC; and 

        WHEREAS,
MPC LLC has duly authorized the execution and delivery of this First Supplemental Indenture pursuant to Section 1201(a) of the Indenture, to evidence the succession of
MPC LLC to MPC, and the assumption by MPC LLC of the covenants of MPC contained in the Indenture and the Securities issued thereunder, and 

        WHEREAS,
MPC LLC has requested the Trustee join with it in the execution of this First Supplemental Indenture; 

        NOW,
THEREFORE, THIS FIRST SUPPLEMENTAL INDENTURE WITNESSETH: 

        For
and in consideration of the premises, it is mutually covenanted and agreed, for the equal and proportionate benefit of all Holders of the Securities or of any series thereof, as
follows: 

 
 

ARTICLE ONE
  
    Covenants and Agreements of MPC LLC.    
  

        Section 101.    MPC LLC hereby expressly assumes the due and punctual payment of the principal of and premium, if any,
and interest, if any, on all Outstanding Securities issued under the Indenture and the performance of every covenant of the Indenture on the part of MPC to be performed or observed. 

 
 

ARTICLE TWO
  
    Section 201. Miscellaneous Provisions.    
  

        Section 1.    The terms defined in the Indenture shall, for all purposes of this First Supplemental Indenture, have the meaning specified in the
Indenture. 

        Section 2.    The
Trustees hereby accept the trusts herein declared, provided, created or supplemented and agree to perform the same upon the terms and conditions herein
and in the Indenture set forth and upon the following terms and conditions: 

        The
Trustees shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this First Supplemental Indenture or for or in respect of the recitals
contained herein, all of which recitals are made by MPC LLG solely. In general, each and every term and condition contained in this First Supplemental Indenture shall apply to and form part of the
Indenture with the same force and effect as if the same were set forth in full with such omissions, variations and insertions, if any, as may be appropriate to make the same conform to the provisions
of this First Supplemental Indenture. 

        Section 3.    Whenever
in this First Supplemental Indenture any of the parties hereto is named or referred to, this shall, subject to the provisions of the Indenture, be
deemed to include the successors 

 

and assigns of such respective parties, and all the covenants and agreements in this First Supplemental Indenture contained by or on behalf of MPC LLC, or by or on behalf of the Trustee shall,
subject as aforesaid, bind and inure to the respective benefits of the respective successors and assigns of such parties, whether so expressed or not. 

        Section 4.    Nothing
in this First Supplemental Indenture, expressed or implied, is intended, or shall be construed, to confer upon, or to give to, any person, firm or
corporation, other than the parties hereto and the holders of the Securities Outstanding under the Indenture, as amended and supplemented, any right, remedy or claim under or by reason of this First
Supplemental Indenture or any covenant, condition, stipulation, promise or agreement hereof, and all the covenants, conditions, stipulations, promises and agreements in this First Supplemental
Indenture contained by or on behalf of respective parties shall be for the sole and exclusive benefit of the parties hereto, and of the Holders of the Securities now or to be Outstanding under the
Indenture. 

        Section 5.    This
First Supplemental Indenture may be executed in several counterparts, each of which shall be deemed to be an original and all of which shall
constitute but one and the same instrument. 

2

 

        IN
WITNESS WHEREOF, the parties hereto have caused this Indenture to be duly executed, and their respective seals to be hereunto affixed attested, all as of the day and year first above
written. 

	[Seal]	 	 	 
	 	 	THE MONTANA POWER, L.L.C.
	

 	
 	
By:	

/s/  JERROLD P. PEDERSON      

	 	 	Name:

Title:	Jerrold P. Pederson
 Vice President, Chief Financial

Officer and Treasurer
 

	ATTEST:	 
	

 	
 	

/s/  PATRICK T. FLEMING      
	

 
	Name:

Title:	 	Patrick T. Fleming
 V.P., General Counsel & Secretary
 	 

	[Seal]	 	 	 
	

 	
 	

THE BANK OF NEW YORK, Trustee
	

 	
 	

By:	

	 	 	Name:

Title:	 

	ATTEST:	 
	

 	
 	

 
	

 	
 	

	

 
	 	 	Name:

Title:	 

3

  

	 
	 

	

STATE OF MONTANA	

)
	 	) ss.:
	COUNTY OF SILVER BOW	)

        On
the 13th day of February, 2002, before me personally came Jerrold P. Pederson, to me known, who, being by me duly sworn, did depose and say that she/he is Vice President, Chief
Financial Officer and Treasurer of the Montana Power, L.L.C., the limited liability company described in and which executed the foregoing instrument; that she/he knows the seal of said company; that
the seal affixed to said instrument is such corporate seal; that it as so affixed by authority of the Board of Directors of said corporation, and that she/he signed her/his name thereto by like
authority. 

	 	 	 	/s/  SUE L. MORGAN      

	 	 	 	Notary Public

[Notarial Seal]

1

 

        IN
WITNESS WHEREOF, the parties hereto have caused this Indenture to be duly executed, and their respective seals to be hereunto affixed attested, all as of the day and year first above
written. 

	

[Seal]	
 	

 	

 
	

 	
 	
THE MONTANA POWER, L.L.C.
	

 	
 	
By:	

	 	 	Name:

Title:	 

	ATTEST:	 
	

 	
 	

 
	

 	
 	

	

 
	 	 	Name:

Title:	 

	[Seal]	 	 	 
	

 	
 	
THE BANK OF NEW YORK, Trustee
	

 	
 	

By:	

/s/  MARYBETH A. LEWICKI      

	 	 	Name:

Title:	MaryBeth A. Lewicki
 Vice President
 

	ATTEST:	 
	

 	
 	

 
	

 	
 	

/s/  MICHAEL PITFICK      
	

 
	Name:

Title:	 	Michael Pitfick

Assistant Treasurer

	 

2

 

	 
	 

	

STATE OF NEW YORK	

)
	 	) ss.:
	COUNTY OF NEW YORK	)

        On
the 13th day of February, 2002, before me, William J. Cassels, a Notary Public in and for the State of New York, personally came and appeared before MaryBeth A. Lewicki,
to me known to me to be a /the Vice President of THE BANK OF NEW YORK, the corporation that executed the within instrument, and acknowledged to me that such corporation executed the same, and being by
me duly sworn, did depose and say that she/he resides at 80 McClean Avenue, Staten Island, New York 10305; that she/he is a /the Vice President of THE BANK OF NEW YORK, the corporation described in
and which executed the within and above instrument; that she/he knows the seal of said corporation; that the seal affixed to said instrument is such corporate seal; that it was so affixed by authority
of the Board of Directors of said corporation, and that she/he signed her/his name thereto by like authority. 

        IN
WITNESS WHEREOF, I have hereunto subscribed my name and affixed my official seal the day and year in this certificate firsts above written. 

	

 	
 	

 	

/s/  WILLIAM J. CASSELS      

	 	 	 	William J. Cassels

Notary Public, State of New York

No. 01CA5027729

Qualified in Bronx County

Commission Expires May 16, 2002

3

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Exhibit 4.2(y)

THE MONTANA POWER, L.L.C. TO THE BANK OF NEW YORK Trustee

FIRST SUPPLEMENTAL INDENTURE (For Unsecured Subordinated Debt Securities relating to Trust Securities)

RECITALS

ARTICLE ONE Covenants and Agreements of MPC LLC.

ARTICLE TWO Section 201. Miscellaneous Provisions.

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