There was success and failure in the last episode of "The Strain". However, one important discovery was made which might be the key to stopping the strigoi but may also lead the rebels into danger.

In episode 3, Ephraim Goodweather (Corey Stoll) and Alex Green (Angel Parker) were able to infect the strigoi's tank of blood with an infected concoction. When the blood was delivered to the abandoned house full of strigoi, they unknowingly fed off a contaminated supply. All the parasitic creatures died as Goodweather and Green checked the premises.

Even better, as they investigated the hideout, Goodweather came across schedules and pick-up points of something The Master (Jonathan Hyde) and the Partnership have been planning for a while now. It was hinted that it could be more blood tanks or something new entirely.

In the trailer for the upcoming episode, Goodweather and Green will continue to uncover the secret plan behind the Partnership. However, because of their hit on the abandoned the house, the Master was able to track their location. The teaser showed that Goodweather and his group will get ambushed by the strigoi and will have to find a way to escape that encounter.

The promo also revealed that Dutch Velders (Ruta Gedmintas) may be imprisoned in some kind of breeding facility. Velders will continue to investigate and at the same time, will try to find a way to escape.

In the last episode, Velders had a chance to flee the facility but took pity on a struggling inmate. Instead of her getting into a box to be shipped out of the place, she let that inmate take her place. However, they got captured and Velders remains there still. She may have to strike a deal with the administrator Sanjay Desai (Cas Anvar) to leave the facility.

"The Strain" season 4 episode 4 will hit the airwaves on Sunday, Aug. 6 at 10 p.m. EDT on FX.