If Lhaereth the Stained is truly attempting to perfect the Great Plague, Mithrandir wants you to learn how far along she has gotten in the process.
'Your descriptions of Agarnaith tell me that Lhaereth's experiments have had an adverse effect upon her land. It may be that a study of the plants and creatures within it will shed light upon her progress, ${PLAYER}.
'We need to learn how near Lhaereth has gotten to achieving her goal. Return to Agarnaith and take samples of material from the animals, plants, and water of that land. You should retain the kingsfoil; combine it with the samples and see if there is any effect. We need not be overly concerned until the kingsfoil ceases to affect the disease, but by then it may be too late. Sixty samples should be enough.
'You know Harthalín. She intended to venture to Agarnaith. Look for her in the swamp north of the eastward-running road to Kala-gijak and I am certain she will aid you in this.'
Harthalín is north of the eastward-running road in Agarnaith, on the way to Kala-gijak.
Mithrandir asked you to collect samples from the plants, animals, and water in Agarnaith in order to determine the progress of Lhaereth's experiments.
Harthalín is by the eastward-running road in Agarnaith.
Harthalín shot an arrow at an Orc attempting to pass north-east of her location in Agarnaith. She wants you to see if it still lives.
Harthalín is by the eastward-running road in Agarnaith.