"Exactly. Fortunately, it worked both ways. In the past, Severus only protected me because he was my mum's best friend. When I told Tom about him being a spy, he had little chance to follow me instead of him since Tom would have never let him go. Also, he had given up so much, I found that I wanted him by my side. But ... well, he's very headstrong. I had to assure his loyalty through non-magical means because Lord Voldemort had already proven that with him, magic was all but useless."