In December, Marissa Mayer poached a star exec from Amazon. He's already quit and gone back.

Yahoo CEO Marissa Mayer likes to brag about what she calls "boomerang" hires - people who used to work at Yahoo, quit, and then came back after she took over.

This is a story about a boomerang hire that went in the wrong direction.

In December 2014, Mayer scored a big win. From Amazon, she poached a new vice president to oversee Yahoo's mobile engineers. His name's Jon McCormack.

Here's his photo:

McCormack was a big deal at Amazon. He worked for Lab126, which is responsible for Amazon's hardware, and oversaw the entire 1,5oo-person group that developed software for the company's various Kindle gadgets. His responsibilities were everything from Kindle apps to e-reader operating systems to the operating system for the Fire Phone, Fire Tablet, and Fire TV.

One person who worked closely with McCormack at Amazon speculates that he made more than $1 million per year, and that when he left Amazon, he left behind millions of dollars in Amazon stock.

Because of the failure of Amazon's Fire Phone, there has been some speculation that McCormack was fired from Amazon. A person who worked with him says that's not true - that Amazon CEO Jeff Bezos personally trusts McCormack very much.

The point being: McCormack wasn't going to come cheap to Yahoo. Fortunately for him, Yahoo has shown it is willing to pay up for executives it wants to hire.

And so McCormack came, and it was big victory for a company that desperately needs talent.

The victory did not last long. McCormack is already out of Yahoo and back at Amazon.

Here's what McCormack's boomerang journey looked like on Facebook.

First came this update in January:

Then, less than two months later, came this update. Note that it was "liked" by Minoo Aya, a recruiter at Amazon:

Then, on March 6, came this update. It's not clear what it means, but a couple friends say "welcome back."

Finally, there's this update. A friend of McCormack's writes, "I'm so confused."

LinkedIn says that McCormack was only at Yahoo for two full months - January and February.

A person close to Yahoo executives says he was actually only at the company for a handful of weeks, maybe two or three.

What went wrong?

We're told by this person that McCormack came in, met with everyone, and decided that Yahoo's mobile group needed some big changes.

This source says that Yahoo's head of mobile, Adam Cahan, disagreed with these changes.

McCormack went back to Amazon. He's now the Chief Technology Officer of Amazon Devices, which sounds similar to what he was doing before, although it's a different job title.

We're told by a person briefed on the details of his return to Amazon that McCormack was not fired by Yahoo.

McCormack is somewhat brash, the source who worked closely with him at Amazon told us. He's a wildlife photographer. He spends a lot of time in third world countries. He runs a charity that builds schools in Africa. He's Australian, and talks about how he used to shoot crocodiles when he was growing up.

Meanwhile, Adam Cahan is considered by many to be difficult to get along with. I heard a lot about Cahan doing the reporting for a book I published a book about Yahoo, called "Marissa Mayer and the Fight to Save Yahoo!"

Sources for the book told me that Cahan is a screamer, and that he's quick to take credit for the work of others. An infamous example inside Yahoo is how he went on stage to accept a design award from Apple for Yahoo's weather app, even though it had not originally been his idea or project.

Yahoo and Amazon declined to comment on this story. Jon McCormack did not respond to requests for comment.

Disclosure: Jeff Bezos is an investor in Business Insider through his personal investment company Bezos Expeditions.