A brazen upstate Army chaplain made a British woman his sex toy to “spice” up his boring marriage and threatened to kill her when she wanted to break away, officials said yesterday.

Capt. John Lau, 50, told a military court he took Amanda Tyler into his Fort Drum home, turned her into his “second wife,” “married” her in a mock Niagara Falls service, and took her to live with his real wife and family.

But Tyler, 34, described the ordained Southern Baptist minister as a sexual sadist who controlled and terrified her.

“The price for objections is severe. If you object, you pay, because he’s ‘The Master,’ ” she told the Watertown Daily Times.

She charged he even wanted her to work as a prostitute to pay for schooling.

Lau, who was jailed yesterday, admitted that he met Tyler in 2004 while stationed in England and brought her to the United States.

“My wife and I were in a lull in our relationship and looking for something to spice up our sexual relations,” Lau told the court.

Tyler lived at his home as his “second wife,” Lau said, and took vacations with the family to Cyprus, the Caribbean and the Florida Keys.

Lau routinely took both women to official functions and introduced Tyler as his “wife’s friend,” he testified during a general court-martial at the upstate base Thursday.

He said Tyler wanted to live with the couple indefinitely in an “exclusive relationship.”

But in September, while Lau was deployed in Iraq with the 10th Marine Division, Tyler told the rest of Lau’s family that she planned to move out.

Lau admitted that he responded in three e-mails to Tyler, threatening to kill her.

Tyler said the sex was consensual but took place “under duress.” She said Lau lured her into the relationship with promises of emotional stability and a life in the United States.

“It wasn’t like I just fell in love with them and decided to be ‘the second wife,’ ” Tyler said. “What I thought they were doing was putting me on the straight and narrow, restoring my confidence.”

She said she didn’t try to complain to the Army or civilian authorities because she was “petrified.”

Ironically, Lau was featured in the base newspaper last June in an article about the virtues of a marriage retreat arranged by the Army at Lake Placid.

“It is important to help them ease marital issues so they can better focus on the mission,” he told The Fort Drum Blizzard.

At his court-martial Thursday, Lau was convicted of adultery and making a threat.

He was sentenced to 14 months in military prison, but under the terms of his plea bargain, he will serve only five months.

Lau was also stripped of his rank and dismissed from the Army, with all pay and allowances forfeited.

With Post Wire Services

andy.soltis@nypost.com