Here is the full list of all 15 Lord Winklebottom Investigates achievements.
Finished the game.
Reached the epilogue.
Reached act 3.
Successfully fake a seance.
Find motives for every character.
Have Frumple perform an autopsy.
Reached act 2.
Read all about Inspector Waffles.
Reached act 1.
Get Salty Walters out of the pub.
Picked up all the litter.
Made tea using tea first.
Made tea using milk first.
Eat the plant in front of Pumphrey.
Complete the game without asking for Frumple's advice.