Inside the Greenhouse, make a beeline for the computer room at the end of the hall. Access the shipping records to find that Craven has been shipping some plants to Richard Aiken, the Hardy Boys' employer. To know which plant that is, look for the extract code corresponding the plant Fer C21 (which will be HH3333). As soon as you log on, a security alert will sound off. If you get caught by the workers, you're dead - so better make sure you duck for cover right away.
How do you do this? Once you get outside, immediate go to the plant right outside the computer room door. This is the HH3333 plant, the one you're looking for. Grab a sample and from there, try and get to the exit without attracting any attention. So turn around, and go towards the right wing and keep going forward. Waverly, the guard who's been constantly buzzing you in will be patrolling the area. Follow him around and turn left to the middle aisle. Use the green fog to your advantage as you won't be seen if you do. If you keep going forward you'll see the guy spraying the fog doing his round. Wait for him to turn right before heading forward. Now turn right, you should be at the left wall by now and the spray guy should be visible as well. When he heads back to the center, go straight to the front wall. Waverly will be there, follow him until you spot the exit to your left. Unless you plan on getting caught, I suggest you make a run for that exit and head back to camp.