Cal. Code of Civil Procedure - CCP § 387. Section 387.
(a)
For purposes of this section:
(1)
“Defendant” includes a cross-defendant.
(2)
“Plaintiff” includes a cross-complainant.
(b)
An intervention takes place when a nonparty, deemed an intervenor, becomes a party to an action or
proceeding between other persons by doing any of the following:
(1)
Joining a plaintiff in claiming what is sought by the complaint.
(2)
Uniting with a defendant in resisting the claims of a plaintiff.
(3)
Demanding anything adverse to both a plaintiff and a defendant.
(c)
A nonparty shall petition the court for leave to intervene by noticed motion or ex parte application. The petition shall include a copy of the proposed complaint in intervention or answer in intervention and set forth the grounds upon which intervention rests.
(d)
(1)
The court shall, upon timely application, permit a nonparty to intervene in the action or proceeding if either of the following
conditions is satisfied:
(A)
A provision of law confers an unconditional right to intervene.
(B)
The person seeking intervention claims an interest relating to the property or transaction that is the subject of the action and that person is so situated that the disposition of the action may impair or impede that person’s ability to protect that interest, unless that person’s interest is adequately represented by one or more of the existing parties.
(2)
The court may, upon timely application, permit a nonparty to intervene in the action or proceeding if the person has an interest in the matter in litigation, or in the success of either of the parties, or an interest against both.
(e)
If leave to intervene is granted by the court, the intervenor shall do
both of the following:
(1)
Separately file the complaint in intervention, answer in intervention, or both.
(2)
Serve a copy of the order, or notice of the court’s decision or order, granting leave to intervene and the pleadings in intervention as follows:
(A)
A party to the action or proceeding who has not yet appeared shall be served in the same manner for service of summons pursuant to Article 3 (commencing with Section 415.10) of Chapter 4 of Title 5 of Part 2.
(B)
A party who has appeared in the action or proceeding, whether represented by an attorney or not represented by an attorney, shall be served in the same manner for service of summons pursuant to Article 3 (commencing with Section 415.10) of Chapter 4 of Title 5 of Part 2, or in the manner
provided by Chapter 5 (commencing with Section 1010) of Title 14 of Part 2.
(f)
Within 30 days after service of a complaint in intervention or answer in intervention, a party may move, demur, or otherwise plead to the complaint in intervention or answer in intervention in the same manner as to an original complaint or answer.