Workout

Warm-up (600)
200 swim
200 kick
200 pull

Set (1800)
Swim - 4 x 100 @ :30 RI 
Descend 1-3  to 400 pace. #4 EZ 
Swim - 400 Free (fast) 
 
Swim - 4 x 50 EZ Choice @ 1:30 
Swim - 200 Free (fast)
 
Swim - 4 x 50 EZ Choice @ 1:30 
Swim - 100 Free (fast)
 
Swim - 4 x 50 EZ Choice @ 1:30 
Swim - 50 Free (fast)
 
Swim - 50 EZ Warmdown 

Set
400 pull
...negative split

Warm-down
200 EZ