Cormac frowned, not liking the idea at all. "Look Cass, I'm going to level with you." He leaned forward and continued. "Percy was very adamant that no one else be involved in this, and I'm pretty sure that would include Susan." In fact, he was almost one hundred percent that Percy would be against Bones' involvement at all.
"There can be no hint of impropriety in this investigation. No matter what my findings, it won't look right that your best friend had access to these private papers, and that she gave me access. What's to stop Umbridge from implicating Susan?" His voice was very serious. "So, I either get an independent curse breaker to let me in, or you give me the spell access yourself. There's really no other option."