You wish you’d never done it.

If only you could hit “reset,” take it all back or call do-overs; you wouldn’t make the same choices. You’d think things through and pay better attention. Instead, now you’ve got regrets you can’t fix but, as in the new novel “I Am Pilgrim” by Terry Hayes, (c.2014, Emily Bestler Books, $26.99 / $29.99 Canada, 613 pages) you can sure try …

There weren’t many times when he wished he hadn’t written the book.

The book was supposed to be cathartic: every case, death and crime he’d ever worked put to paper so he could focus on forgetting them all, published by an esoteric press under a nom de plume because he had no name.

You don’t get to be Rider of the Blue—the top of the top in a department the government officially denied—by holding onto things like names.

Months were spent pouring out observations for an audience he knew would be small, detectives and operatives mostly, and he rarely regretted it. Not, anyhow, until he saw the aftermath of a perfect murder committed by someone who used what he’d written to kill.

He immediately felt guilt. Then he felt revulsion when he recognized a series of numbers scrawled on a clue as an area code for Turkey. He wasn’t eager to revisit memories attached to numbers like that. He was even less interested in going back to the Turkish town where he’d been a freshman agent but when the president of the United States asks, you do what’s required.

American forces had recently discovered something that made the president’s blood run cold: in a remote area of Afghanistan, three bodies were found buried in quicklime and infected with a virus that was hand-engineered to bypass vaccines. It had potential for mass devastation that would make the Black Plague look like a children’s game. And it was obvious that its creator, a man he nicknamed Saracen, was ready to use it.

The agent wasn’t happy about coming out of retirement, but he was the best chance anyone had of catching a madman. He would start in Turkey; he’d require fake passports, a faux life, and yet another identity. He told the president to call him “Pilgrim.”

Whatever you’re doing right now, stand up and turn around. Take a good look at the edge of your seat. That’s where you’ll be clinging when you read “I Am Pilgrim.”

Beginning with a body in an acid bath, author Terry Hayes flings us from New York to Paris, to New England, the Middle East and everywhere in between. He takes you back to the past and a future that’s so chillingly realistic you’ll want to bar the doors.

Our host is a taciturn man who officially doesn’t exist but who’s quietly known as someone who finishes a job, no matter what it takes.

And what it takes, well, look at your seat again.

This is a thriller in the finest form, perfect for poolside, park, or plane ride. You’ll understand why, once you read “I Am Pilgrim,” and you’ll be glad you’ve done it.