The diagram on the right comes from Alexander Graham Bell’s private laboratory notebook dated March 9, 1876. Bell would use the pictured device to famously call to Watson in the next room the very next day on March 10th. The diagram on the left inset is a confidential filing at the U.S. Patent Office made by inventor Elisha Gray almost three weeks earlier. Gray was Bell’s main rival in the race to develop the telephone. The similarity of these two documents—strongly suggesting Bell’s plagiarism of Gray’s invention—launched me unexpectedly into “a vexing intrigue at the heart of one of the world’s most important inventions.”.