Here is the full list of all 15 If On A Winter's Night, Four Travelers achievements.
Finish Act I.
Finish Act II.
Finish Act III.
FInish Act IV.
Give Patrick back his watch.
Call Patrick a cab.
Play the harp.
Read all the books in the parlour.
Give Mr Williams his morphine.
Check in on Mrs Williams on the Other Side.
Examine all the shelves in the library.