The lost last page

Excuse me’
‘Yes, madame, how may I help’
‘I bought this book from here yesterday and I wish to exchange it.’
‘I’m sorry. We’re not a library, madame.’
‘You don’t understand. This ‘who done it’, is missing the last page.’
‘Then It’s damaged goods, lady.’
‘I agree’
‘I can’t see how I can help you. You can’t prove that the page was missing when it left the store..’
‘The last page holds the solution to the whole story. It’s driving me mad not knowing.’
The manager picks up a new copy and begins to read the last page out loud.