The Testament of William S. is the twenty-fourth album of the comic series Blake and Mortimer, written by Yves Sente and drawn by André Juillard, based on the characters created by Edgar P. Jacobs.

That same evening, Captain Blake and Professor Philip Mortimer go to the Royal Albert Hall to attend a performance with William Shakespeare's The Merchant of Venice.

The next day, Sarah Summertown, president of the William Shakespeare Defenders Society, is made aware of the discovery and the Marquis's butler leaves for London to deliver the documents by hand.

At the same time, the Earl of Oxford, who defends the idea that it is his ancestor Edward de Vere who is the true author of the work of Shakespeare, learns the news and decides to enlist the services of Olrik, currently imprisoned in Wandsworth.

Sarah Summertown then explains to Blake and Mortimer the value of the discovery: in 1858, Lord Lupus Sandfield made the promise to donate a sum now representing 10 million pounds to whoever discovers a proof of the true authorship of the work of Shakespeare.

Mortimer and Elizabeth return to London and, thanks to a scheme developed by MI5, manage to save the work from the hands of Sharkey and Freddy who are waiting for them at the exit of the airport.

The manuscript could not be considered as valid proof by the notary because it was still an unsigned draft, but Sarah is pleased to have discovered the truth about Shakespeare and a financial agreement has been made with Lord Sandfield.