You might like Carl Humphries’ The Piano Handbook. This is the book I wish I had been available when I was a teenager and gave up on a bad teacher who insisted on my playing only from a five finger exercise book when I wanted to learn Bach Inventions (which I then did on my own). Only quite a few years later was I able to study with a good teacher.
This is an excellent book for a serious, disciplined student who is experienced in learning from books. It is not for the faint of heart, but it will repay diligent study. It starts at the very beginning with hand position, correlating the keyboard with sheet music notation and a discussion of rhythm and note values. But it moves quickly thereafter into basic theory (scales, key signatures, intervals, chords). The emphasis is on playing beautiful short original classical pieces, with a couple of brief excursions into jazz and other styles. You’ll learn about pedaling, how to listen, articulation (legato, staccato, etc.) expression in music, and many other topics. Everything you need (except a piano) is included in the book - all the sheet music for pieces and other exercises and a very nice CD performed by the author of all the music he includes.
Amazon.com has 83 reviews for the 2002 edition (mostly 4- and 5-star) They will tell you more that I could in many pages here, so be sure to look at them to see if this book is what you had in mind when you asked for an “adult” book. I thought that the book’s explanations were very clear, but you can always ask questions on this forum if there’s something you don’t understand.
The 2007 edition is the one that Amazon.com handles through a reseller - price around $30. I have the 2002 edition. The 2007 may be the same book, just a different printing and not a new edition. I emailed the author to ask about this before posting here, but have received no reply.
Best wishes with your piano adventure.