LANCASTER (CBS) — A San Diego woman was arrested Friday in a Lancaster neighborhood after her bizarre plot to kill the wife and child of the man she allegedly loved was foiled.

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Lancaster police said Deirdre Allen planned to kill the woman and 3-year-old boy and make it look like a murder-suicide. They said she documented the steps of her murder plan on tape.

Authorities said Allen arrived at the victim’s home at 43230 Gadsen Avenue Friday morning wearing white construction coveralls and a face mask. She also had a fake gun and gloves.

“The suspect thought she was home alone with her toddler son. She normally would have been, but luckily she wasn’t,” said Lancaster police Sgt. Robert Rush.

Police say a struggle ensued between Allen and several of the victim’s family members who happened to be at the home. Allen was later wrestled to the ground and as they waited for authorities to arrive, family members discovered the murder plot on tape with detailed steps on how to kill the victims.

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“Step one, said calm yourself down,” the tape said according to a family member.

Police also found a white substance near the home’s door that is believed to be poison. Officials said Allen’s plan was to force the woman to drink it.

“We believe she was going try to suffocate the toddler to make it look like a murder suicide,” Sgt. Rush said.

Allen was arrested for attempted murder.

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Police did not disclose the relationship between Allen and the child’s father.