This all becomes a moot point because, much like in that Simpsons episode where the town historian keeps finding more lines on the town-charter parchment, the wiretap on Hank's office keeps playing, and Hank has called up the FBI and asked them if they might have done something as stupid as attaching a tracker to the outside of a barrel at Madrigal. The agent is like "Uhhh ... why, did someone find it?"
Lydia and Jesse are relieved, but Mike still obviously wants to kill her, just because. Not least of which is the newly relayed information that the Feds put trackers on EVERY barrel at Madrigal, meaning the methylamine is completely off limits to them now. Jesse agrees with Lydia's assertion that she actually saved their asses by spotting the tracker, but Mike is done trusting her. He tells Walt and Jesse about how she put a hit out on him, which takes both men aback (Jesse: "Like the MAFIA?"). Lydia starts yelling something about methylamine, about how she can still hook them up. Not with the barrels in the warehouse, of course. She's talking about "an ocean of the stuff."
After the break, we see Jesse has convinced Mike to let Walt talk to Lydia about this little plot of hers; to "trust" Walt, so you can imagine how well that goes over. Inside, Lydia wants Walt to swear on his children's lives that they won't kill her. As a trust exercise, Walt wants to know if she really put a hit out on Mike; she says yes, and the reason why once again brings up the thorny issue of the hush payments they're shelling out to Mike's associates. Lydia doesn't know it, but she and Walt are on the same side of this issue. She doesn't trust that those imprisoned men will remain quiet; they know everything about her and some of them know about Walt, the master chemist. Walt takes this in and then changes the subject to the ocean of methylamine. [Note: But not without at first telling Lydia that she has no leverage here and he is, as always, the one who knocks, natch.]
Cut to Lydia presenting her plan to all three men. She lays out a map (convenient!) and explains that a train leaves Long Beach at 3:00 PM, destined for Flagstaff and parts beyond. If that train is pulling a tanker full of 24,000 gallons of methylamine passes through a dead stretch of New Mexico desert where they'll be cut off from any and all communications, how stupid do three drug dealers have to be to try to rob it? Show your work. Jesse's like, "Rob it? Like Jesse James?" Lots of love for ol' JJ these last few episodes. Mike thinks this is all a quick way to have the three of them thrown in jail for the rest of their lives. So Lydia explains the concept of this stretch of "dark territory," where any of the train's usual fail-safe alarms and other communications to control will not be operational -- no cell service either. The fact that Lydia has to preface this info dump with "what you don't know, and I do, because my job requires me to keep track of my buyers' shipments" makes me think the writers were at least a little aware of how contrived this whole plot could seem.