'One of the most successful MI5 undercover surveillance officers of his time' Sun Tom Marcus spent years of his life undercover, waging a secret war on the streets against those who want to do us harm. Now, for the first time, he tells the full story of what it is like to live your life in the shadows and who you need to become to survive. First published in 2016, Soldier Spy was a series of stories from Tom's years in MI5 and has now sold over 250,000 copies across all editions and was a Sunday Times bestseller for five months. I Spy takes us even deeper into the ongoing battle to keep us all safe.