The take-away message? Don't lean in too far.
"Full Circle: A Memoir of Leaning In Too Far and the Journey Back" is a cautionary tale to women about putting their careers first.
Callan recounts how lost she felt after leaving Wall Street, according to a Bloomberg review of the memoir. She describes Christmas Eve in 2008, after she'd left Lehman for Credit Suisse, when she tried to overdose on sleeping pills.
This isn't the first time that Callan - who now goes by Callan Montella after marrying her high-school classmate, Anthony Montella - has issued this type of warning to women.
In 2013 she wrote an op-ed in The New York Times about work/life balance for women.
"I didn't start out with the goal of devoting all of myself to my job. It crept in over time. Each year that went by, slight modifications became the new normal," she wrote at the time. "Inevitably, when I left my job, it devastated me."
Now Callan, 50, is married and has a one-year-old child. She says her life has come "full-circle."
According to a Fortune review, some lessons Callan writes are: Don't do something just because you're good at it, and know what you're leaning into. She says for example that she was ill-equipped to take the CFO job, but didn't want to turn it down.
The National Archives recently released transcripts, meeting agendas, and confidentiality agreements from the Financial Crisis Inquiry Commission, including an interview with Callan giving her side of Lehman's collapse.