We've provided written directions, plus a map and screenshot. If you're after the whole lot, search for the Secrets methodically in the order presented by our guide as you clear them through - or borough by borough in whatever order you please.
The in-game numbering is a mess, but we've included a reference so you can quickly find any you're missing. Interact with the box (Circle/B) to collect the key inside. They look like small wooden boxes, highlighted white with Eagle Vision, and make a sound like a music box when you're close enough. There are Secrets of London scattered throughout London. Completing this challenge unlocks the Aegis, a powerful and very cool-looking outfit for Evie. Perhaps the toughest challenge Assassin's Creed Syndicate offers is tracking down the Secrets of London. Track down all the Secrets of London with our borough-by-borough illustrated guide.