In the clip, we see the detectives going over what little evidence they've been able to recover from the Roxxon explosion. As you'll recall, in the second episode, Peggy tells Jarvis he needs to get rid of Stark's car as it was damaged and bits were left back at the explosion site. In this upcoming third episode, we see the detectives starting to piece things together - and it isn't long before things lead back to Howard Stark.
Don't forget to watch AGENT CARTER tomorrow at 9PM EST. (This will be its normal slot now as it officially fills AGENTS OF S.H.I.E.L.D.'s time-slot.)