The funny thing was, the shower story was true. Never mind the part where she'd omitted Bill being present.
At her mother's cool tone, Tonks shot Bill an apologetic look and set her hand on her mother's elbow. "Mum, it's fine, don't be like that. Bill's the one who brought me in. Probably saved my life, you know, so you could at least be nice to him."
That, of course, was a gross exaggeration - she would've woken up wet and dizzy eventually - but it might buy Bill a little goodwill in the face of her mother inevitably putting the pieces together. Friends didn't just randomly find other friends knocked unconscious in the shower, after all. Maybe if she got lucky, her mother might buy the 'we were drinking last night, and I crashed on his couch' story, but based on her otherwise atrocious luck that morning, that was highly unlikely.
She gave Bill a small smile. "Thanks for waiting - you didn't have to do that. Aren't you going to be..." She glanced at the clock on the wall and frowned. "Aren't you already late for work?"