Alan Turing broke the German naval Enigma, designed the machine you are almost certainly holding or sitting in front of, invented the test that still frames every argument about artificial intelligence, and explained why leopards have spots. He was prosecuted for being who he was, given hormone injections instead of prison, and died at forty-one beside a half-eaten apple that nobody thought to test.

Thinking Machines tells that story, but it argues something most accounts leave out. Turing proved the same thing twice. In 1936 he showed that computation does not require understanding. In 1952 he showed that form does not require a designer. Everything in between—the codebreaking, the chess program he ran by hand at half an hour a move, the question he refused to answer and replaced instead—belongs to one idea, followed with unusual stubbornness across a short life.

Boris Kriger takes the listener from a schoolboy writing about what holds the spirit to the machines now sitting on the other side of our conversations, insisting that meaning is made out there in the world and not confessed from inside. Along the way he clears out the myths that have grown over the story—the Churchill quotation nobody said, the computer Turing did not build, the suicide that was never established — and finds the man underneath: funny, difficult, kind, a serious marathon runner who cycled to work in a gas mask, who buried his savings in a wood and could not decode his own directions for finding them again.

The result is a book about a mathematician who kept asking better questions than the ones he was handed, and about the one question he honestly set aside, which is still sitting there, waiting.