1. Be prepared to zap a rocket turret with your Electro Bolt before entering. A solitary Splicer is also waiting in here.
2. Loot a corpse near the turret and use Telekinesis to pull an EVE Hypo and cash from a high ledge to the left. Find Mariska Lutz's audio diary Shouldn't Have Come on a rock under the Rolling Hills sign ahead/right.
3. Approach the Metro door and a yellowish chemical falls from above. Ryan is poisoning the plant life in Rapture, eliminating the city's oxygen supply. Find a Handbag and Liquid Nitrogen above the yellow "Rapture Metro" sign on the left.
4. Atlas tells you to find a scientist named Julie Langford. Fortunately, her laboratory is just to the left of the Metro access. Hack or destroy a security camera on the right, and find an Ammo Bandito machine to the left.
5. Listen to Langford and receive a new goal, which can be completed back at the Waterfall Grotto.
6. Head to the Waterfall Grotto, directly across from the Gatherer's Garden we were at a while ago. Several groups of Splicers stand in your way, so have Enrage! handy. My Research Camera also proved useful -- snapping shots of a wandering Rosie netted me the Photographer's Eye 2 Combat Tonic. Thuggish Splicer shots earned me the SportBoost 2 Physical Tonic.
7. Enter the Waterfall Grotto and find this Security Evasion Physical Tonic. (This tonic is not here if you visit the Grotto earlier.) Andrew Ryan's audio diary The Market Is Patient is seen on the bench. A U-Invent machine is to the left next to a corpse with some crafting items. You'll also find a Grenade Launcher and several Heat-Seeking RPGs.
8. The downstairs area is wired for sound so proceed cautiously. These traps can be disabled with Telekinesis. Avoid a flamethrower turret behind the left wall.
9. Two turrets are on either side of the room; here they are battling it out after I hacked the one on the left. Proximity Mines are near the left turret and a security camera is in the far-left corner.
10. Andrew Ryan's Offer A Better Product audio diary is found here.
11. Julie Langford's Early Tests Promising audio diary can be found on this crate. Turn around and follow a tunnel to the flamethrower turret and more supplies, then grab a rose from this bush to complete Langford's objective.
12. Frag Grenades, a First Aid Kit and Potato Chips are under the security camera on the left. Electro Bolt the door control on the right to find a roll of Film, an EVE Hypo, Antipersonnel Auto Rounds and Diane McClintock's audio diary Heroes and Criminals. This room is a good place to hide out while your hacked turrets and security bots decimate the spawning Splicers.
13. Return to Langford's lab. Listen to what she has to say then use the Pneumo to complete the objective and open the door. A Hacking Expert Engineering Tonic is on the desk, and Langford's audio diary What Won't They Steal? is to the right. Chlorophyll Solution is above the file cabinet.
14. Head through the door on the right and Langford gives you a countdown to make it upstairs before the turrets reactivate. Find her audio diary Teaching An Old Hound here. You've got plenty of time, so search the area thoroughly and hack the Health Station, U-Invent and Circus of Values.
15. When you're ready to move on, approach the Securis door to open it then ascend the stairs.
16. You'll find Langford in her office upstairs. But so does Ryan.
17. After the gas subsides and the doors open, enter Langford's office and search her body for The Lazarus Vector audio diary. Note that she has scribbled the code 9457 onto the window. A new weapon, the Chemical Thrower, and one of its ammo types, Liquid Nitrogen, are on the table behind you.
18. Search the desk on the left for crafting items and use the Botanical Illustration to reveal a wall safe. Code 9457 nets you Langford's Lazarus Vector Formula audio diary, and the key to Farmer's Market.
19. You get a new multi-part goal, requiring seven Distilled Water, Enzyme Samples and Chlorophyll Solution.
20. A pair of Splicers are waiting as you backtrack through the lab. Enrage! is my alpha-strike preference. Napalm, the Chemical Thrower's fire ammo, is ahead/right, and a security camera is to its left. You'll be returning later so hack away for future assistance.
21. A Houdini Splicer attacks. Antipersonnel Auto rounds tear him up. Don't forget to snap some photos. Chlorophyll will likely be found on Houdini bodies for a while.
22. A Houdini Splicer attacks. Antipersonnel Auto rounds tear him up. Don't forget to snap some photos. Chlorophyll will likely be found on Houdini bodies for a while.
23. Snap some photos of the nearby turret before hacking it.
24. I found Napalm in this previously-empty file cabinet before leaving the laboratory.
25. A Splicer is waiting for you outside. I Enraged him and he went suicidal on a nearby Big Daddy.
26. We need to head to Farmer's Market, but first there is a short optional diversion. Julie Langford's audio diaries have mentioned a strange sect of cultists. Find her audio diary The Saturnine just inside this cave entrance to give them a name.
27. Chlorophyll is here by the makeshift altar. Ready your camera and weapon of choice against a Houdini Splicer.
28. The Houdini attacks as you approach the cave exit. He'll likely have Chlorophyll on his body.
29. Be sure to continue your Houdini research to earn improved Houdini detection, allowing you to hear and see Houdinis well before they materialize.
30. Upstairs is this second Saturnine cave entrance.
31. Enter to find Chlorophyll here on the right.
32. Another Houdini attacks. I'm out of Antipersonnel Auto Rounds but regular Machine Gun Rounds get the job done, too. Search his body for more Chlorophyll and you should have reached your target of seven by now. Don't forget to search the nearby Steamer Trunk.
33. Exit left then backtrack through this Arcadia Glens door.
34. Continue through this Tree Farm entrance, clear of the vegetation that was blocking it before Ryan's defoliant was released.
35. Enrage! this Splicer and he'll attack his own security bot.
36. Julie Langford's Arcadia And Oxygen audio diary is found here.
37. Find this EVE Hypo on the ledge straight ahead. Buckshot can be found by jumping the stair-like beams on the left to reach the small landing upper-right.
38. Continue through this doorway.
39. Save your ammo as the Splicer approaches. He'll succumb to the flames without any assistance. Upgrade your weapon of choice at the Power to the People station on the left.
40. I continue my Machine Gun specialization by choosing Machine Gun Damage.
41. Find Potato Chips and a Storage Crate at the top of the stairs, and a First Aid Kit and Circus of Values on the left. Have your Research Camera ready before you battle this female Houdini Splicer.
42. I was able to complete my Houdini Splicer research, earn Increased Damage +++ and get the Achievement.
43. Search this Trash Can for supplies and don't miss the two Pep Bars just visible ahead/left.
44. This safe can be found on the far left.
45. Tenenbaum's Maternal Instinct audio diary is found here.
46. Find a corpse and a Shotgun before entering the bulkhead to Farmer's Market. You'll have another odd flashback before reaching the door.