Three people in a field of brown plants.
Three people investigate why the plants are dying in the field.
People can be in a field for reasons other to investigate something.  Also, brown plants do not mean that something is dying.
exists s1 x1 x2 x3.(a_topic(x1) & in(x1,x2) & of(x2,x3) & n_plant(x3) & a_brown(s1) & Theme(s1,x3) & n_field(x2) & n_people(x1) & card_eq_3(x1))
exists x1 x3 x4.(n_field(x4) & n_plant(x3) & exists e2 e1 x2.(n_reason(x2) & Topic(e2,e1) & Actor(e2,x1) & v_investigate(e2) & reason_rel(e1,x2) & in(e1,x4) & Actor(e1,x3) & v_die(e1)) & n_people(x1) & card_eq_3(x1))