Now Museum, Now You Don't

An old man Lupin meets by chance turns out to be the grandson of Ukiyoe master Tooshuusai Sharaku. In order to test his own skill he has been switching his own works for Sharaku's originals, but suffered a heart attack just as he was about to make the last switch. At Fujiko's request, and after much trouble, Lupin succeeds in acting as Sharaku III's stand-in. But the old man has already died by that time. Where have the Ukiyoe gone?