Jessica Carney was his granddaughter - she's the basis for the little girl character in An Adventure In Time And Space - and has made a good honest effort to get under the skin of the grandfather she knew only as a stressed elderly man, who turned into a hero on television. The 180 pages of narrative reach Doctor Who only on page 154, which actually shows a rather admirable sense of proportion; Hartnell's life was much more than Who.
And it was a tough life. His father is unknown, and his unmarried mother was pretty much absent. (His birth family were not completely estranged - he remained in touch with his second cousin Norman Hartnell throughout their lives.) As a boy he eked out a life of expulsions from numerous schools and petty crime. In his teenage years the good-looking rough lad was adopted by the art connoisseur Hugh Blaker, who sent him to acting school and got him onto an upward track generally.
And from then on Hartnell steadily carved out a line in serious supporting parts (see eg here, esp from 1:22:00, or here with Jon Pertwee and George "Minder" Cole) with occasional glimpses of greater things as mentioned above (though even in Carry On Sergeant he had to fight for top billing with the young Bob Monkhouse). He remained very insecure, pursuing younger women, fussing about food and cooking, drinking when he wasn't working (which was more often than he liked). His wife Heather, who had grown up next door to John Masefield in Oxford, was a serious creator in her own right, both as actress and playwright; one of her plays was filmed.
Doctor Who was much the best thing that ever happened to William Hartnell professionally, and reading this second hand account is irresistibly reminiscent of reading the first-hand account of that other intriguingly flawed character, Tom Baker, for whom Doctor Who was a redemptive experience, enabling him to be reincarnated from sinner to hero. Hartnell, who was never religious as far as we can tell, lapped up his new connection with his young audience, and perhaps soldiered on longer than he should have because he was loving it too much.
Doctor Who now goes back almost 51 years, but in 1963 it had no history at all; and its future rested on Hartnell's own 38 years as an actor. I would have liked Carney to dig a little more into, say, how and why Hartnell's career differed from those of his contemporaries - he was born in the same year as John Mills, Rex Harrison, Michael Redgrave and Robert Morley (all of whom started acting professionally after he did, but came from more privileged social backgrounds). But I think this book is quite a good explanation of how and why he ended up in the role for which he is best known, and how and why he played it the way that he did, setting up the programme for a longevity he could not have imagined.