Sherlock takes the large book down from the top shelf. The anthology is massive, weighty. It's a study of Italian horticulture, in Italian, and it's several hundred years old. He keeps it on the top shelf with the other antique tomes because he knows no one will give it a second look (he's come home to find John perusing the ancient book of medical oddities that rests just to its right only twice, and he himself has referenced the lithograph of poisonous plants shelved to the left a handful of times over the past few months).
He has never read the book on Italian horticulture. It's not that he can't, he absolutely could if he were so inclined, he's just not interested. He pauses to study the worn leather binding, and he's glad there is little chance John will wake long enough to walk in on him with the book - a ten-hour shift at the surgery followed by a gruesome overnight murder case that spilled into most of the next day ensures John will sleep soundly for at least another four hours.
No, ownership of the book of Italian horticulture has nothing to do with an interest in gardening. It's not scientific curiosity, nor a desire to immerse himself in the language. It's nothing so noble, nor is it logical. Sherlock is embarrassed to admit, even just to himself, what this book represents. It's the very embodiment of sentiment.
Placing the volume carefully on the coffee table, Sherlock gingerly turns through the brittle pages until he comes across the first of many delicate secrets he's hidden within. It's a perfectly dried and pressed daisy, a gift from a neighbor girl, one of few childhood friends. He trails his fingers over it so very gently before he moves to the next.
A pink bush rose from mummy's garden. A white carnation from his grandmother's funeral. A little bundle of hawthorn from a particularly pleasant family holiday to the country. A red poppy from the first time he paid a young homeless girl for information on a potential suspect.
There are other occasions and memories, dozens of them, all stored safely in Sherlock's book of Italian horticulture, each one represented by a perfectly dried and pressed flower. There are also several poisonous blossoms preserved amongst the pages, strictly for safekeeping and future reference.
The newest additions to Sherlock's collection are all from cases. A great many of them are specific to John-related memories. He thinks that is probably significant, but hasn't brought himself to explore the line of thought in depth. It's not that he doesn't want to understand this enigma of a man more fully, but he's afraid of what he might discover if he does.
So he stores details about John in his mind palace, and he presses mementos in his book. He finds an empty page and carefully positions a fiery red oak leaf from their post-case walk through the park only a few hours prior. Despite being exhausted, they'd been laughing together about nothing in particular. They'd stopped for a coffee at a vendor cart. When John turned to hand him his cup he had smiled warmly and plucked the errant leaf from Sherlock's hair.
"Autumn's always been my favorite," John stated, apropos of nothing, before he let the leaf flutter to the ground.
Sherlock convinces himself, relying on the most dubious evidence, that John hadn't noticed him retrieve the leaf and tuck it carefully away in his pocket. He makes a note of the date on the page, though he knows he will never need the reference.