Possible Clues:

• Nameless doctor noticing ring
• Hiding one’s identity
• Humble worker in pub, taking it over under a false name
• Anonymous(ly)
• In disguise, strangely noticing nothing
• Using false name
• With your identity concealed
• Using pseudonym, noticing anagrams with surprised cry?
• Doctor noticing source of oedema is unidentified
• Doctor noticing Oscar's assumed identity