(CNN) Maritza Castillo and her husband were on their way to help a family member -- but they ended up saving the life of a stranger.

The couple was on Interstate-10 in Houston on Tuesday, en route to pick up Castillo's brother who'd been flooded in.

But the pair couldn't reach him because the roads were submerged.

"We got turned around," Castillo told CNN by phone.

As they waited in stalled traffic, they watched a horrifying scene unfold in front of them.

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