All 6 Uses of

intervene
in
The Phantom of the Opera

She was unable to explain this phenomenon, which was not new to her, except by the intervention of the ghost.†
Chpt 4 *

intervention = get involved; or come between

"I understand," he said, "that no human being can sing as you sang the other evening without the intervention of some miracle.†
Chpt 5

A few weeks later, when the tragedy at the Opera compelled the intervention of the public prosecutor, M. Mifroid, the commissary of police, examined the Vicomte de Chagny touching the events of the night at Perros.†
Chpt 5

The stranger kept up the gesture that recommended discretion and then, at the moment when the astonished viscount was about to ask the reason of his mysterious intervention, bowed and disappeared.†
Chpt 15

And Mme. Giry caught Mr. Manager Richard a mighty box on the ear, before Mr. Manager Moncharmin had time to intervene.†
Chpt 16

intervene = get involved or come between

Definitions:

(1) (intervene as in: intervened in the war)
the process of getting involved to influence an outcome
The exact meaning of intervention can depend upon its context. For example:
- "intervention program for at-risk youth" -- a process of trying to influence the direction of someone's life
- "medical intervention" -- action taken to improve a medical outcome
- "military intervention" -- interference by a government in affairs of another government (in this case to interfere militarily)
- "had a family intervention" -- an organized meeting of family members to encourage someone (who is often surprised) to recognize and work at solving a problem such as substance abuse
(2) (intervene as in: in the intervening years)
something between two other things -- especially the passage of time between two events
(3) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Much more rarely, intervene can mean:
in various senses, including:
- to verbally interrupt -- as in "Not now!' she intervened."
- to be physically between -- as in: "You can't walk from one hill to the other because an impassable river intervenes."