In his new book, former FBI deputy director Andrew McCabe offers extensive new details of investigators' fateful January 2017 interview with former national security adviser Michael Flynn at the White House -- a breezy conversation which began, according to McCabe, with all the urgency of a "playdate."

McCabe wrote in “The Threat,” released Tuesday, that "one thing [Flynn] said stands out in my memory" -- namely that "when I told him that people were curious" about his conversations with the then-Russian Ambassador Sergey Kislyak, Flynn replied, "You know what I said, because you guys were probably listening."

Without confirming Flynn's suspicions, McCabe wrote: "I had to wonder, as events played out: If you thought we were listening, why would you lie?" (A Washington Post article published one day before Flynn's White House interview with the agents, citing FBI sources, publicly revealed that the FBI had wiretapped Flynn's calls and cleared him of any criminal conduct.)

According to McCabe, the interview was "very odd" because "it seemed like [Flynn] was telling the truth" to the two agents who interviewed him, including since-fired FBI agent Peter Strzok. Flynn, the interviewing agents told McCabe, "had a very good recollection of events, which he related chronologically and lucidly," did not appear to be "nervous or sweating," and did not look "side to side" -- all of which would have been "behavioral signs of deception."

McCabe wrote that Flynn seemed "completely normal" -- even when, on three occasions, Flynn looked at the window and told agents, "What a beautiful black sky."

McCabe maintained that Flynn made that memorable comment three times -- first, at "noon," then an hour later, and then one more time shortly after that. However, McCabe's timeline in the book appeared to contradict the sentencing memorandum filed late last year by Flynn's attorneys, citing government documents.

The memorandum, which relied on sealed documents whose authenticity was not challenged by Special Counsel Robert Mueller's team, asserted that McCabe had called Flynn to set up the interview at 12:35 p.m. on Jan. 24, 2017, and that agents arrived at the White House at 2:15 p.m. -- more than two hours after McCabe claimed in the book that Flynn first made the comment to the agents about the "beautiful black sky."

It was unclear if McCabe was suggesting that Flynn made the "big blue sky" comment literally, or whether McCabe instead was using a metaphor. The remark does not appear in quotes in McCabe's book.

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McCabe was fired last year for multiple violations of the FBI's ethics code, including lying to fellow FBI officials, and Flynn -- facing other potential charges related to his overseas lobbying work -- declared in his guilty plea nearly 11 months after his interview that he had knowingly lied to FBI agents. Flynn sold his house in Virginia amid mounting legal fees leading up to his plea deal.

Flynn was never charged with wrongdoing as a result of the substance of his calls with Kislyak.

In a post-interview meeting in McCabe's office, the agents "weren't saying they believed [Flynn], and they weren't saying they didn't believe him." McCabe said the interviewers "struck me as being mainly surprised by the encounter" and "the difficulty of resolving their observations," because "what he said was in absolute, direct conflict with the information that we had."

Setting up the interview, McCabe wrote, was effortless, as Flynn brushed off the need for a lawyer to be present. In a bombshell court filing last December, Flynn's legal team noted that McCabe had suggested the Justice Department would need to get involved if Flynn sought to involve the White House Counsel or a personal lawyer -- a claim McCabe confirmed in his book.

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"The tone was as friendly, and as detached, as if we were planning a playdate for our kids," McCabe wrote.

The former FBI deputy director noted that then-Acting Attorney General Sally Yates thought there was "good reason to believe Flynn had lied to [Vice President Mike Pence] concerning his communications with Kislyak as of Jan. 12. Pence had appeared on national television and vouched for Flynn, saying that Flynn had explained that his communications with Kislyak did not, in any way, involve the sanctions that had been imposed by the Obama administration.

Nevertheless, McCabe said, the FBI decided that while it seemed "plausible" that Flynn was liable to be blackmailed by Russia, the concern "did not seem imminent enough to warrant disrupting the ongoing investigative work." The FBI did, however, respond to the DOJ's "sense of urgency" by "hastening the FBI's own work," including the Flynn interview.

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During the interview, Flynn told the agents "not really" when asked if he had sought to convince Kislyak not to escalate a brewing fight with the U.S. over sanctions imposed by the Obama administration, according to a FD-302 witness report released last year.

Flynn issued other apparently equivocal responses to FBI agents' questions, and at various points suggested that such conversations might have happened or that he could not recall them if they did, according to the 302. The 302 indicated that Flynn was apparently aware his communications had been monitored, and at several points he thanks the FBI agents for reminding him of some of his conversations with Russian officials.

After the interview, Yates went to the White House to explain her concerns, McCabe wrote.

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Flynn's legal future remains uncertain. At a fiery hearing in December, Judge Emmet G. Sullivan suggested Flynn should be tried for treason before walking back his comments. He set a status conference for Flynn's sentencing on Mar. 13 -- a significant delay he said was necessary to assess Flynn's cooperation with a separate ongoing criminal case involving foreign lobbying violations in Turkey.

The date of Flynn's ultimate sentencing is undecided, pending that status conference.

Also in the book, McCabe rails against President Obama’s attorney general, Loretta Lynch, for her decisions and actions while the FBI investigated Hillary Clinton’s use of a private email server during the 2016 campaign, saying Lynch should have been recused from the probe and a special counsel should have been appointed.

McCabe said Lynch, after the outcry over the meeting, should have stepped away from the probe – which was code-named "Midyear Exam" by the FBI.

“She should have recused herself from Midyear at that point,” McCabe wrote. “She did not — she made things worse.”

Fox News' Alex Pappas contributed to this report.